This fixes the issue where if the migration tries to migrate an already
scheme-aware member object it would end up removing it's scheme-derived
roles.
Instead, only if the member object is unmigrated do we default to
setting the scheme-derived role booleans to false. We tell if it is an
unmigrated member object by checking if the booleans are set to null.
* MM-9728: Online migration for advanced permissions phase 2
* Add unit tests for new store functions.
* Move migration specific code to own file.
* Add migration state function test.
* Style fixes.
* Add i18n strings.
* Fix mocks.
* Add TestMain to migrations package tests.
* Fix typo.
* Fix review comments.
* Fix up the "Check if migration is done" check to actually work.
* Add Scheme model and stub store.
* Port ChannelStore to be Scheme aware.
* Make almost all the API/APP layer work with ChannelSchemes.
Only thing still hacky is UpdateChannelMemberRoles().
* Add basic SchemeStore implementation.
* Migrate UpdateChannelMemberRoles properly and fix tests.
* Update store tests and mocks so they work.
* Include creating default roles in Scheme create store function.
* Implement role deletion and start scheme deletion.
* Only use non-deleted roles for authorization.
* Add GetByScheme method to Team store.
* Add GetChannelsByScheme.
* Update store mocks.
* Implement scheme deletion in the store.
* Rename is valid function.
* Add offset and limit to queries to fetch teams and channels by scheme.
* Fix queries.
* Implement scheme awareness in Team store and add a migration.
* Tidy up ChannelStore mapping functions and add exhaustive unit tests.
* Add all missing i18n.
* Proper tests for TeamStore internal functions and fix them.
* Make additional TeamMember fields nullable.
* Make new ChannelMember fields nullable.
* Create new nullable columns without defaults.
* Make new fields in large tables nullalble.
* Fix empty list of TeamMembers.
* Deduplicate SQL queries.
* Fix spelling.
* Fix review comment.
* More review fixes.
* More review fixes.
