Disable chat metric report when async exeuction.

Author: wenjin272

python/flink_agents/plan/actions/chat_model_action.py

@@ -192,6 +192,8 @@ async def chat(
     for attempt in range(num_retries + 1):
         try:
             if chat_async:
+                # TODO: Support report metrics in async thread
+                chat_model.set_metric_group(None)
                 response = await ctx.durable_execute_async(chat_model.chat, messages)
             else:
                 response = chat_model.chat(messages)