MM-44221: Add admin console setting to enable/disable App Bar (#20224)

* Revert "[MM-39820] Add AppBarEnabled feature flag (#18967)"

This reverts commit ba1b279c5f.

* Add EnableAppBar admin setting

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/config.go

@@ -949,6 +949,7 @@ type ExperimentalSettings struct {
 	CloudBilling                    *bool   `access:"experimental_features,write_restrictable"`
 	EnableSharedChannels            *bool   `access:"experimental_features"`
 	EnableRemoteClusterService      *bool   `access:"experimental_features"`
+	EnableAppBar                    *bool   `access:"experimental_features"`
 }
 
 func (s *ExperimentalSettings) SetDefaults() {
@@ -987,6 +988,10 @@ func (s *ExperimentalSettings) SetDefaults() {
 	if s.EnableRemoteClusterService == nil {
 		s.EnableRemoteClusterService = NewBool(false)
 	}
+
+	if s.EnableAppBar == nil {
+		s.EnableAppBar = NewBool(false)
+	}
 }
 
 type AnalyticsSettings struct {