head-management: add brightness-info-v1 extension

src/tasks/connector.rs

@@ -68,6 +68,7 @@ pub fn handle(state: &Rc<State>, connector: &Rc<dyn Connector>) {
         color_space: backend_state.color_space,
         transfer_function: backend_state.transfer_function,
         supported_formats: Default::default(),
+        brightness: None,
     };
     let data = Rc::new(ConnectorData {
         id,