feat: Add isWaitingForAgentResponse property to TaskViewModel

- Added a boolean property `isWaitingForAgentResponse` to the `TaskViewModel` class to track whether a task is being created and waiting for a response from the agent.
- When a task is being created, we set `isWaitingForAgentResponse` to `true` and notify the listeners.
- When the task creation process is completed (successfully or not), `isWaitingForAgentResponse` is set to `false` and listeners are notified.
- Updated the `ChatView` class to listen to changes in `TaskViewModel.isWaitingForAgentResponse` to show the loading indicator conditionally.

frontend/lib/views/chat/chat_view.dart

@@ -64,7 +64,7 @@ class _ChatViewState extends State<ChatView> {
   @override
   Widget build(BuildContext context) {
     // TODO: Do we want to have a reference to task view model in this class?
-    final taskViewModel = Provider.of<TaskViewModel>(context, listen: false);
+    final taskViewModel = Provider.of<TaskViewModel>(context, listen: true);
     return Scaffold(
       body: Column(
         children: [
@@ -105,7 +105,8 @@ class _ChatViewState extends State<ChatView> {
           LoadingIndicator(
               isLoading: Provider.of<TaskQueueViewModel>(context, listen: true)
                       .isBenchmarkRunning ||
-                  widget.viewModel.isWaitingForAgentResponse),
+                  widget.viewModel.isWaitingForAgentResponse ||
+                  taskViewModel.isWaitingForAgentResponse),
           const SizedBox(height: 10),
           // Input area
           Padding(