[MM-15296] Migrate "Preference.Save" to Sync by default (#10866)

* response format changes

* Generated mocks
Fixed all references of Preferences.Save

* Remove old code from store.go (incorrect merge)

* Review change - Add validations on count and error

* Review change - return from root level

* Review change - return 0 as nil value for int

* fix initialisation of err in preference_store

app/preference.go

@@ -48,9 +48,9 @@ func (a *App) UpdatePreferences(userId string, preferences model.Preferences) *m
 		}
 	}
 
-	if result := <-a.Srv.Store.Preference().Save(&preferences); result.Err != nil {
-		result.Err.StatusCode = http.StatusBadRequest
-		return result.Err
+	if _, err := a.Srv.Store.Preference().Save(&preferences); err != nil {
+		err.StatusCode = http.StatusBadRequest
+		return err
 	}
 
 	message := model.NewWebSocketEvent(model.WEBSOCKET_EVENT_PREFERENCES_CHANGED, "", "", userId, nil)