Add feature flag for apps (#16851)

* Add feature flag for apps

* Update default to false

* Add plugin version Feature Flag

* Fix typo

* Only force shutdown, and leave the enable status dependant on the user (defaulting to enable)

* Remove unneeded tracking of status

* Handle plugin init on startup for locally installed plugin

app/plugin.go

@@ -97,6 +97,13 @@ func (a *App) SyncPluginsActiveState() {
 				pluginEnabled = state.Enable
 			}
 
+			// Tie Apps proxy disabled status to the feature flag.
+			if pluginID == "com.mattermost.apps" {
+				if !a.Config().FeatureFlags.AppsEnabled {
+					pluginEnabled = false
+				}
+			}
+
 			if pluginEnabled {
 				enabledPlugins = append(enabledPlugins, plugin)
 			} else {

app/plugin_install.go

@@ -373,6 +373,9 @@ func (a *App) installExtractedPlugin(manifest *model.Manifest, fromPluginDir str
 	// Activate the plugin if enabled.
 	pluginState := a.Config().PluginSettings.PluginStates[manifest.Id]
 	if pluginState != nil && pluginState.Enable {
+		if manifest.Id == "com.mattermost.apps" && !a.Config().FeatureFlags.AppsEnabled {
+			return manifest, nil
+		}
 		updatedManifest, _, err := pluginsEnvironment.Activate(manifest.Id)
 		if err != nil {
 			return nil, model.NewAppError("installExtractedPlugin", "app.plugin.restart.app_error", nil, err.Error(), http.StatusInternalServerError)