Define an additional pattern for resource references.

[rofrankel]

This PR assumes that we will adopt http://aip.dev/157 without substantial changes.

📑 Proposed changes

Adds a new resource association pattern to aep.dev/resource-association. This pattern supports use cases where server-side dereferencing of resource references is desirable (filtering, GraphQL-style retrieval, etc.).

🍱 Types of changes

What types of changes does your code introduce to AEP? Put an x in the boxes
that apply

• Enhancement
• New proposal
• Migrated from google.aip.dev

📋 Your checklist for this pull request

Please review the AEP Style and Guidance for
contributing to this repository.

General

• Basic Guidance is met.
• Ensure that your PR
  references AEPs
  correctly.

Additional checklist for a new AEP

• A new AEP should be no more than two pages if printed out.
• Ensure that the PR is editable by maintainers.
• Ensure that File structure
  guidelines are met.
• Ensure that
  Document structure
  guidelines are met.

💝 Thank you!

[toumorokoshi]

Thanks! some specific discussion points to start.

[toumorokoshi]

great, thanks!