MM-45009: Delete ThreadMemberships from "left" channels (#22559)

* MM-50550: Filter out threads from "left" channels v2

Currently leaving a channel doesn't affect the thread memberships of
that user/channel combination.
This PR aims to filter out all threads from those channels for the user.

Adds a DeleteAt column in the ThreadMemberships table, and filter out
all thread memberships that are "deleted".
Each time a user leaves a channel all thread memberships are going to be
marked as deleted, and when a user joins a channel again all those
existing thread memberships will be re-instantiated.

Adds a migration to mark all existing thread memberships as deleted
depending on whether there exists a channel membership for that
channel/user.

* Added migration files into list

* Fixes tests

* Fixes case where DeleteAt would be null

* Guard thread API endpoints with appropriate perms

* Deletes ThreadMembership rows upon leaving channel

* Minor style changes

* Use NoTranslation error

* Refactors tests

* Adds API tests to assert permissions on Team

* Adds tests, and fixes migrations

* Fixes test description

* Fix test

* Removes check on DM/GMs

* Change the MySQL query in the migration

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/db/migrations/migrations.list

@@ -212,6 +212,8 @@ channels/db/migrations/mysql/000105_remove_tokens.down.sql
 channels/db/migrations/mysql/000105_remove_tokens.up.sql
 channels/db/migrations/mysql/000106_fileinfo_channelid.down.sql
 channels/db/migrations/mysql/000106_fileinfo_channelid.up.sql
+channels/db/migrations/mysql/000107_threadmemberships_cleanup.down.sql
+channels/db/migrations/mysql/000107_threadmemberships_cleanup.up.sql
 channels/db/migrations/postgres/000001_create_teams.down.sql
 channels/db/migrations/postgres/000001_create_teams.up.sql
 channels/db/migrations/postgres/000002_create_team_members.down.sql
@@ -424,3 +426,5 @@ channels/db/migrations/postgres/000105_remove_tokens.down.sql
 channels/db/migrations/postgres/000105_remove_tokens.up.sql
 channels/db/migrations/postgres/000106_fileinfo_channelid.down.sql
 channels/db/migrations/postgres/000106_fileinfo_channelid.up.sql
+channels/db/migrations/postgres/000107_threadmemberships_cleanup.down.sql
+channels/db/migrations/postgres/000107_threadmemberships_cleanup.up.sql