* fix posts returned from unread API when the list contains parent post/s
* add ExtendAll to PostList and update test per feedback
* revert unintentional change to the other test and fix comment
* update the existing postlist.Extend, filter unique values and update unit tests
* [MM-11210] Add API GET 'api/v4/channels/{channel_id:[A-Za-z0-9]+}/posts/unread' for scrolling overhaul (#9108)
* Add API GET 'api/v4/channels/{channel_id:[A-Za-z0-9]+}/posts/unread'
* add constants
* refactor GetPostSince and added more tests
* move constants to app package
* [MM-11528 && MM-11583] Add userId to in the "posts/unread" path and update test with time delay to fix intermittent failure (#9229)
* add userId to in the "posts/unread" path and update test with time delay to fix intermittent failure
* add limit before and after to query
* remove time delay on test and put pretermined value of Post.CreateAt
* Fix conflict
* [MM-11876] Add cursor to posts list such as next_post_id and previous_post_id (#9707)
* add cursor to posts list such as next_post_id and previous_post_id
add publish previous_post_id on WEBSOCKET_EVENT_POSTED and only get next or previous post IDs if necessary
revert change on adding previous_post_id in WEBSOCKET_EVENT_POSTED
add missing strings import
fix merge conflicts
* update per comment
* update per feedback
* corrected the logic in getting the next and previous post ID
* fix logic to determine next and post IDs, and rename function to have suffix of "Time"
* rearrange logics and add mote tests
* fix merge conflict
* fix missing message when using unread API (#10233)
* MM-15569 Fixes failing test on TestGetPostsForChannelAroundLastUnread (#11039)
* Fix missing posts when getting posts since
* revert changes to GetPostsSince
* migrate Post.GetPostAfterTime and Post.GetPostBeforeTime to sync by default
* revert change to cacheItem
* Fix post ID validation, build query on squirrel and only return post ID as necessary
* image proxy support
* go vet fix, remove mistakenly added coverage file
* fix test compile error
* add validation to config settings and documentation to model functions
* add message_source field to post
* Implement POST /posts endpoint for APIv4
* Implement GET /channels/{channel_id}/posts endpoint for APIv4
* Implement GET /posts/{post_id} endpoint for APIv4
* Implement GET /posts/{post_id}/thread endpoint for APIv4
* Skip team get if it's a DM channel in handlePostEvents
