Prior to this commit, we had two places that need to know the nuances
ofquerying for tag flares and what we should include in our queries for
serialization.
With this commit, we're factoring towards a common source of knowledge
and providing a much needed test for the expected output of this
serialization.
Loosely related to #15916, #15983, #15994, and #16032.
* Re-order test cases to increase tests readability
* Add user_id filter for articles query
* Add organization_id and tags filters
* Add new params to SearchController#feed_content
* Add current_user param so that it can be tested for a small pool of users
