MM-8796: Full implementation of "Schemes" in Store/Model/App layers. (#8357)

* 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.

store/sqlstore/store.go

@@ -52,6 +52,7 @@ type SqlStore interface {
 	DoesTableExist(tablename string) bool
 	DoesColumnExist(tableName string, columName string) bool
 	CreateColumnIfNotExists(tableName string, columnName string, mySqlColType string, postgresColType string, defaultValue string) bool
+	CreateColumnIfNotExistsNoDefault(tableName string, columnName string, mySqlColType string, postgresColType string) bool
 	RemoveColumnIfExists(tableName string, columnName string) bool
 	RemoveTableIfExists(tableName string) bool
 	RenameColumnIfExists(tableName string, oldColumnName string, newColumnName string, colType string) bool
@@ -88,4 +89,5 @@ type SqlStore interface {
 	Plugin() store.PluginStore
 	UserAccessToken() store.UserAccessTokenStore
 	Role() store.RoleStore
+	Scheme() store.SchemeStore
 }