Python: Request cancellation sample (#459)

* request cancellation via tasks

* fix missing kwargs

python/samples/getting_started/chat_client/chat_response_cancellation.py

@@ -0,0 +1,19 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+import asyncio
+
+from agent_framework.openai import OpenAIChatClient
+
+async def main():
+    chat_client = OpenAIChatClient()
+
+    try:
+        task = asyncio.create_task(chat_client.get_response(messages=["Tell me a fantasy story."]))
+        await asyncio.sleep(1)
+        task.cancel()
+        await task
+    except asyncio.CancelledError:
+        print("Request was cancelled")
+
+if __name__ == "__main__":
+    asyncio.run(main())