chore(galaxy): Operation for retrieving authorized identities

[betimshahini]

Description

Implements Galaxy operation to retrieve authorized identities for an application, identified through the API key.

Returns identityURN, name and imageURL for each entry.

Note: connected accounts won't be returned as those can be retrieved proactively on a per-user basis through the standard /userinfo endpoint, or reactively per-change-event through future work done under #2621

Related Issues

• Closes feat(galaxy): Return a list of all users associated with an app #2716

Testing

• Make graphql call to getAuthorizedIdentities() with a galaxy API key issued for an app with authorized users.
• Validate same users appear as the ones in users listing in Console for same app

Checklist

• I have read the CONTRIBUTING guidelines
• I have tested my code (manually and/or automated if applicable)
• I have updated the documentation (if necessary)