added resources for saved filter handling

[mplushnikov]

Description of the change

Added resource and datasource for handling of spacelift saved filter, E.g. to be able to add predefined filters for different teams

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (non-breaking change that adds documentation)

Checklists

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development
• Examples for new resources and data sources have been added
• Default values have been documented in the description (e.g., "Dummy: (Boolean) Blah blah. Defaults to false.)
• If the action fails that checks the documentation: Run go generate to make sure the docs are up to date

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• Pull Request is no longer marked as "draft"
• Reviewers have been assigned
• Changes have been reviewed by at least one other engineer

[peterdeme]

@mplushnikov thanks for the contribution, we'll try to merge it asap. thought we'll need to open another PR for it once again.

[truszkowski]

@mplushnikov I've created a new PR with Your changes. Secrets don't work with forks, so we can't test them properly.

Your changes (from both PRs - this and here) will be merged soon; we're just adjusting to recent changes and reviewing code.

[truszkowski]

Continuation in PR
Thanks @mplushnikov for your contribution ❤️!
The changes look good for me, PR is in review now.
This one I'll close.