feat: optimize output parse (#906)

api/core/agent/agent/output_parser/structured_chat.py

 class StructuredChatOutputParser(LCStructuredChatOutputParser):
     def parse(self, text: str) -> Union[AgentAction, AgentFinish]:
         try:
-            action_match = re.search(r"```(.*?)\n?(.*?)```", text, re.DOTALL)
+            action_match = re.search(r"```(\w*)\n?({.*?)```", text, re.DOTALL)
             if action_match is not None:
                 response = json.loads(action_match.group(2).strip(), strict=False)
                 if isinstance(response, list):
             else:
                 return AgentFinish({"output": text}, text)
         except Exception as e:
-            raise OutputParserException(f"Could not parse LLM output: {text}") from e
+            raise OutputParserException(f"Could not parse LLM output: {text}")