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/app_test.go

@@ -148,6 +148,8 @@ func TestDoAdvancedPermissionsMigration(t *testing.T) {
 			model.PermissionEditBookmarkPrivateChannel.Id,
 			model.PermissionDeleteBookmarkPrivateChannel.Id,
 			model.PermissionOrderBookmarkPrivateChannel.Id,
+			model.PermissionManagePublicChannelBanner.Id,
+			model.PermissionManagePrivateChannelBanner.Id,
 		},
 		"team_user": {
 			model.PermissionListTeamChannels.Id,
@@ -191,6 +193,8 @@ func TestDoAdvancedPermissionsMigration(t *testing.T) {
 			model.PermissionEditBookmarkPrivateChannel.Id,
 			model.PermissionDeleteBookmarkPrivateChannel.Id,
 			model.PermissionOrderBookmarkPrivateChannel.Id,
+			model.PermissionManagePublicChannelBanner.Id,
+			model.PermissionManagePrivateChannelBanner.Id,
 		},
 		"system_user": {
 			model.PermissionListPublicTeams.Id,