Update proposal for custom attributes schema

[melnikovi]

Problem

Current schema for custom attributes doesn't support attributes that can have multiple values (checkbox, multiselect).

Solution

Requested Reviewers

[nrkapoor]

@melnikovi Does this align with the custom attribute proposal from @akaplya for Product? #429

[mslabko]

I think we have to add "type" opinion here to be able to render the appropriate template (datetime, text, multi-select, checkbox ...)

E.g.

"attributes":[
    {
      "code":"multiselect_attribute",
      "type":"multiselect",
      "values":[
            "Option 1",
            "Option 2"
      ]
    }
  ]

[melnikovi]

Attributes are going to be displayed as information and not as fields you can control, so I don't think it's necessary.

[mslabko]

it will be useful to render field properly on UI without complex logic. E.g. for "Date" field - "10-11-2020"

[cpartica]

yes, they are needed for the forms

[paliarush]

We have this data already available in the scope of customAttributeMetadata query. Since update frequency for attribute metadata and product attribute values is different, it makes sense to separate them to avoid excessive payload size.

[cpartica]

even if this adds more complexity, it's the graphql way to do it and I prefer it

[cpartica]

do fragments bring any value for PWA since we still prefer these flat single structure arrays vs infterfaces?

[cpartica]

customAttributesLists - do we need a better name for this

[paliarush]

1. We need to make sure that data and metadata is not mixed in the same queries because they have different life cycles. Metadata can be cached on the client and reused between queries for data.
2. Each schema modification must be covered with the example of usage. Suggestion is to split the original proposal into smaller ones, which address one problem at a time.
3. We need to add proposed schema to the running server to make sure it is syntactically correct. For interfaces we can temporarily use an existing type resolver to bypass errors.