Enhancement Proposal Process (shipwright-io#252)

Port of the OKD enhancement proposal process [1] for the `build` project.
Notable adjustments made for `build`:

* References to "domain" removed.
* Updated directory tree structure.
* Added links to the README with links to the KEP and OKD enhancement processes.

[1] https://github.com/openshift/enhancements/blob/master/guidelines/README.md

docs/proposals/README.md

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+# Enhancement Proposals
+
+An Enhancement Proposal is a way to propose, communicate, and coordinate on new efforts for the `build` project.
+
+It is inspired from our experience with the
+[Kubernetes](https://github.com/kubernetes/enhancements/blob/master/keps/README.md) and
+[OKD](https://github.com/openshift/enhancements/blob/master/guidelines/README.md) enhancement
+processes.
+
+## Quick start
+
+1. Socialize an idea with others. Make sure others think the work is worth doing, and are willing to review design and code changes required.
+2. Draft a proposal by copying the [proposal template](/docs/proposals/guidelines/proposal-template.md).
+3. Submit a pull request with your proposal.
+
+## FAQs
+
+**Do I have to use the process?**
+
+If the enhancement has broad scope, yes.  It helps everyone track why, when, how, and by whom work is done.
+
+**Why would I want to use the process?**
+
+Provide a mechanism to communicate design and implementation strategies across the OKD community.
+
+**My FAQ isn't answered here!**
+
+Open an issue and ask or even better open a PR with a question and proposed answer.

docs/proposals/guidelines/proposal-template.md

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+---
+title: neat-enhancement-idea
+authors:
+  - "@janedoe"
+reviewers:
+  - TBD
+  - "@alicedoe"
+approvers:
+  - TBD
+  - "@oscardoe"
+creation-date: yyyy-mm-dd
+last-updated: yyyy-mm-dd
+status: provisional|implementable|implemented|deferred|rejected|withdrawn|replaced
+see-also:
+  - "/docs/proposals/this-other-neat-thing.md"  
+replaces:
+  - "/docs/proposals/that-less-than-great-idea.md"
+superseded-by:
+  - "/docs/proposals/our-past-effort.md"
+---
+
+# Neat Enhancement Idea
+
+This is the title of the enhancement. Keep it simple and descriptive. A good title can help
+communicate what the enhancement is and should be considered as part of any review.
+
+The YAML `title` should be lowercased and spaces/punctuation should be replaced with `-`.
+
+To get started with this template:
+
+1. **Make a copy of this template.** Copy this template into the main `proposals` directory.
+2. **Fill out the "overview" sections.** This includes the Summary and Motivation sections. These
+   should be easy and explain why the community should desire this enhancement.
+3. **Create a PR.** Assign it to folks with expertise in that domain to help sponsor the process.
+4. **Merge at each milestone.** Merge when the design is able to transition to a new status
+   (provisional, implementable, implemented, etc.). View anything marked as `provisional` as an idea
+   worth exploring in the future, but not accepted as ready to execute. Anything marked as
+   `implementable` should clearly communicate how an enhancement is coded up and delivered. Aim for
+   single topic PRs to keep discussions focused. If you disagree with what is already in a document,
+   open a new PR with suggested changes.
+
+The `Metadata` section above is intended to support the creation of tooling around the enhancement
+process.
+
+## Release Signoff Checklist
+
+- [ ] Enhancement is `implementable`
+- [ ] Design details are appropriately documented from clear requirements
+- [ ] Test plan is defined
+- [ ] Graduation criteria for dev preview, tech preview, GA
+- [ ] User-facing documentation is created in [docs](/docs/)
+
+## Open Questions [optional]
+
+This is where to call out areas of the design that require closure before deciding to implement the
+design. For instance:
+
+> 1. This locks a build strategy to run privileged pods. Should we do this?
+
+## Summary
+
+The `Summary` section is incredibly important for producing high quality user-focused documentation
+such as release notes or a development roadmap. It should be possible to collect this information
+before implementation begins in order to avoid requiring implementors to split their attention
+between writing release notes and implementing the feature itself.
+
+A good summary is probably at least a paragraph in length.
+
+## Motivation
+
+This section is for explicitly listing the motivation, goals and non-goals of this proposal.
+Describe why the change is important and the benefits to users.
+
+### Goals
+
+List the specific goals of the proposal. How will we know that this has succeeded?
+
+### Non-Goals
+
+What is out of scope for this proposal? Listing non-goals helps to focus discussion and make
+progress.
+
+## Proposal
+
+This is where we get down to the nitty gritty of what the proposal actually is.
+
+### User Stories [optional]
+
+Detail the things that people will be able to do if this is implemented. Include as much detail as
+possible so that people can understand the "how" of the system. The goal here is to make this feel
+real for users without getting bogged down.
+
+#### Story 1
+
+#### Story 2
+
+### Implementation Details/Notes/Constraints [optional]
+
+What are the caveats to the implementation? What are some important details that didn't come across
+above. Go in to as much detail as necessary here. This might be a good place to talk about core
+concepts and how they relate.
+
+### Risks and Mitigations
+
+What are the risks of this proposal and how do we mitigate. Think broadly. For example, consider
+both security and how this will impact the larger OKD ecosystem.
+
+How will security be reviewed and by whom? How will UX be reviewed and by whom?
+
+Consider including folks that also work outside your immediate sub-project.
+
+## Design Details
+
+### Test Plan
+
+**Note:** *Section not required until targeted at a release.*
+
+Consider the following in developing a test plan for this enhancement:
+
+- Will there be e2e and integration tests, in addition to unit tests?
+- How will it be tested in isolation vs with other components?
+
+No need to outline all of the test cases, just the general strategy. Anything that would count as
+tricky in the implementation and anything particularly challenging to test should be called out.
+
+All code is expected to have adequate tests (eventually with coverage expectations).
+
+### Graduation Criteria
+
+**Note:** *Section not required until targeted at a release.*
+
+Define graduation milestones.
+
+These may be defined in terms of API maturity, or as something else. Initial proposal should keep
+this high-level with a focus on what signals will be looked at to determine graduation.
+
+Consider the following in developing the graduation criteria for this enhancement:
+
+- Maturity levels - `Dev Preview`, `Tech Preview`, `GA`
+- Deprecation
+
+Clearly define what graduation means.
+
+#### Examples
+
+These are generalized examples to consider, in addition to the aforementioned [maturity
+levels][maturity-levels].
+
+##### Dev Preview -> Tech Preview
+
+- Ability to utilize the enhancement end to end
+- End user documentation, relative API stability
+- Sufficient test coverage
+- Gather feedback from users rather than just developers
+
+##### Tech Preview -> GA
+
+- More testing (upgrade, downgrade, scale)
+- Sufficient time for feedback
+- Available by default
+
+**For non-optional features moving to GA, the graduation criteria must include end to end tests.**
+
+##### Removing a deprecated feature
+
+- Announce deprecation and support policy of the existing feature
+- Deprecate the feature
+
+### Upgrade / Downgrade Strategy
+
+If applicable, how will the component be upgraded and downgraded? Make sure this is in the test
+plan.
+
+Consider the following in developing an upgrade/downgrade strategy for this enhancement:
+
+- What changes (in invocations, configurations, API use, etc.) is an existing cluster required to
+  make on upgrade in order to keep previous behavior?
+- What changes (in invocations, configurations, API use, etc.) is an existing cluster required to
+  make on upgrade in order to make use of the enhancement?
+
+### Version Skew Strategy
+
+How will the component handle version skew with other components? What are the guarantees? Make sure
+this is in the test plan.
+
+Consider the following in developing a version skew strategy for this enhancement:
+
+- During an upgrade, we will always have skew among components, how will this impact your work?
+- Does this enhancement involve coordinating behavior in the control plane and in the kubelet? How
+  does an n-2 kubelet without this feature available behave when this feature is used?
+- Will any other components on the node change? For example, changes to CSI, CRI or CNI may require
+  updating that component before the kubelet.
+
+## Implementation History
+
+Major milestones in the life cycle of a proposal should be tracked in `Implementation History`.
+
+## Drawbacks
+
+The idea is to find the best form of an argument why this enhancement should _not_ be implemented.
+
+## Alternatives
+
+Similar to the `Drawbacks` section the `Alternatives` section is used to highlight and record other
+possible approaches to delivering the value proposed by an enhancement.
+
+## Infrastructure Needed [optional]
+
+Use this section if you need things from the project. Examples include a new subproject, repos
+requested, github details, and/or testing infrastructure.
+
+Listing these here allows the community to get the process for these resources started right away.