Improve Threads beta around degraded mode (#8318)

* Hide MAB Threads prompt if user would have degraded mode

* Confirm user wants to enable Threads beta if in degraded mode

* fix

* Fix copy

src/settings/controllers/SettingController.ts

@@ -46,6 +46,17 @@ export default abstract class SettingController {
         return null; // no override
     }
 
+    /**
+     * Called before the setting value has been changed, can abort the change.
+     * @param {string} level The level at which the setting has been modified.
+     * @param {String} roomId The room ID, may be null.
+     * @param {*} newValue The new value for the setting, may be null.
+     * @return {boolean} Whether the settings change should be accepted.
+     */
+    public async beforeChange(level: SettingLevel, roomId: string, newValue: any): Promise<boolean> {
+        return true;
+    }
+
     /**
      * Called when the setting value has been changed.
      * @param {string} level The level at which the setting has been modified.