ConversationalChatAgent: Allow customizing `TEMPLATE_TOOL_RESPONSE` (#2361)

It's currently not possible to change the `TEMPLATE_TOOL_RESPONSE`
prompt for ConversationalChatAgent, this PR changes that.

---------

Co-authored-by: Dev 2049 <dev.dev2049@gmail.com>

langchain/agents/conversational_chat/base.py

@@ -37,6 +37,7 @@ class ConversationalChatAgent(Agent):
     """An agent designed to hold a conversation in addition to using tools."""
 
     output_parser: AgentOutputParser = Field(default_factory=ConvoOutputParser)
+    template_tool_response: str = TEMPLATE_TOOL_RESPONSE
 
     @classmethod
     def _get_default_output_parser(cls, **kwargs: Any) -> AgentOutputParser:
@@ -99,7 +100,7 @@ class ConversationalChatAgent(Agent):
         for action, observation in intermediate_steps:
             thoughts.append(AIMessage(content=action.log))
             human_message = HumanMessage(
-                content=TEMPLATE_TOOL_RESPONSE.format(observation=observation)
+                content=self.template_tool_response.format(observation=observation)
             )
             thoughts.append(human_message)
         return thoughts