Make frontend non-experimental. https://github.com/Koenkk/zigbee2mqtt/issues/4266

lib/controller.js

@@ -68,7 +68,7 @@ class Controller {
             this.extensions.push(new ExtensionBridge(...args, this.enableDisableExtension));
         }
 
-        if (settings.get().experimental.frontend) {
+        if (settings.get().frontend) {
             this.extensions.push(new ExtensionFrontend(...args));
         }