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/app/platform/web_hub_test.go

@@ -153,6 +153,7 @@ func TestHubSessionRevokeRace(t *testing.T) {
 	time.Sleep(2 * time.Second)
 	// We override the LastActivityAt which happens in NewWebConn.
 	// This is needed to call RevokeSessionById which triggers the race.
+
 	err = th.Service.AddSessionToCache(session)
 	require.NoError(t, err)