* Add v4 endpoint for getting the channels on a team for a user
* Implement PUT /channels/{channel_id}/patch endpoint for APIv4
* Implement POST /teams/{team_id}/channels/search endpoint for APIv4
* Update permission check
* Implement POST /channels/members/{user_id}/view endpoint for APIv4
* Implement PUT /channels/{channel_id}/members/{user_id}/roles endpoint for APIv4
* Implement DELETE /channels/{channel_id}/members/{user_id} endpoint for APIv4
* implement get channels endpoints and updated drivers and unittests
* removed channel deletion on tear down, removed manage permission on get channels endpoints, and updated utils to add constant channel length
* added constants for user, team and channel length, updated context to use the model functions
* make sure team name length should be less than the minimum length and revert underscore to team name validity
* changed post test condition from notfound to unauthorized
* Implement GET /channels/{channel_id}/members
* Implement GET /channels/{channel_id}/members/{user_id} endpoint for APIv4
* Implement /users/{user_id}/teams/{team_id}/channels/members endpoint for APIv4
* Fix unit test
