Make REST and datastore API for creating/retrieving audiences consistent

[jimmymadon]

Feature Description

In #8108, we created a REST endpoint to GET:audiences. As per this comment, we have deviated from our standard convention of returning the primary resource in the backend.

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Do not alter or remove anything below. The following sections will be managed by moderators only.

Acceptance criteria

• The GET:audiences REST endpoint within the Analytics_4 class should return the list of audiences and not the whole Analytics API response directly.
• The datastore action should be updated to return the response so that calling the getAudiences selector still returns the same list of audiences as it does now.

Implementation Brief

• [ ] Within includes/Modules/Analytics_4.php:
  • [ ] In the parse_data_response() method, add a new case to handle the GET:audiences endpoint. Simply return (array) $response->getAudiences()
• [ ] Within assets/js/modules/analytics-4/datastore/audiences.js:
  • [ ] In the fetchGetAudiencesStore reducer callback, simply return audiencesResponse instead of the audiences property within audiencesResponse.

Test Coverage

• No new tests required.

QA Brief

• Follow the QAB for #8108 and verify the getAudiences() selector still works.

Changelog entry

[techanvil]

I've moved this back to Backlog as the final in-progress changes to the design doc, relating to audience caching, will affect the AC for this one.

[techanvil]

Closing this issue, as we'll be removing the GET:audiences endpoint and the getAudiences() selector (see https://github.com/google/site-kit-wp/issues/8487), so this issue will no longer be needed.