fix: adapt openai protocol

Author: tomasliu-agora

realtime_agent/realtime/struct.py

@@ -334,7 +334,7 @@ class Response:
     status: ResponseStatus = "in_progress"  # Status of the response
     status_details: Optional[ResponseStatusDetails] = None  # Additional details based on status
     usage: Optional[Usage] = None  # Token usage information
-
+    metadata: Optional[Dict[str, Any]] = None  # Additional metadata for the response
 
 
 @dataclass
@@ -728,4 +728,4 @@ def parse_server_message(unparsed_string: str) -> ServerToClientMessage:
     raise ValueError(f"Unknown message type: {data['type']}")
 
 def to_json(obj: Union[ClientToServerMessage, ServerToClientMessage]) -> str:
-    return json.dumps(asdict(obj))
+    return json.dumps(asdict(obj))