Channel banner permissions (#30917)

* Fixed save state panel for channel banner

* Defined default background color

* Updated test

* WIP

* wip

* removed unused param

* Updated tests

* CI

* Fixed mmctl test

* Fixed TestDoAdvancedPermissionsMigration test

* Test update

* lint fix

* lint fix

---------

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

server/channels/testlib/store.go

@@ -86,6 +86,8 @@ func GetMockStoreForSetupFunctions() *mocks.Store {
 	systemStore.On("GetByName", "products_boards").Return(&model.System{Name: "products_boards", Value: "true"}, nil)
 	systemStore.On("GetByName", "elasticsearch_fix_channel_index_migration").Return(&model.System{Name: "elasticsearch_fix_channel_index_migration", Value: "true"}, nil)
 	systemStore.On("GetByName", model.MigrationAddSysconsoleMobileSecurityPermission).Return(&model.System{Name: model.MigrationAddSysconsoleMobileSecurityPermission, Value: "true"}, nil)
+	systemStore.On("GetByName", model.MigrationKeyAddChannelBannerPermissions).Return(&model.System{Name: model.MigrationKeyAddChannelBannerPermissions, Value: "true"}, nil)
+
 	systemStore.On("InsertIfExists", mock.AnythingOfType("*model.System")).Return(&model.System{}, nil).Once()
 	systemStore.On("Save", mock.AnythingOfType("*model.System")).Return(nil)