Improvement/add finish reason to generation info in chat open ai (#7478)

Description: ChatOpenAI model does not return finish_reason in
generation_info.
Issue: #2702
Dependencies: None
Tag maintainer: @baskaryan 

Thank you

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

langchain/chat_models/openai.py

@@ -386,7 +386,10 @@ class ChatOpenAI(BaseChatModel):
         generations = []
         for res in response["choices"]:
             message = _convert_dict_to_message(res["message"])
-            gen = ChatGeneration(message=message)
+            gen = ChatGeneration(
+                message=message,
+                generation_info=dict(finish_reason=res.get("finish_reason")),
+            )
             generations.append(gen)
         llm_output = {"token_usage": response["usage"], "model_name": self.model_name}
         return ChatResult(generations=generations, llm_output=llm_output)