re-generate for conversation (#2165)

### What problem does this PR solve?


### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/conversation_app.py

         e, conv = ConversationService.get_by_id(req["conversation_id"])
         if not e:
             return get_data_error_result(retmsg="Conversation not found!")
-        conv.message.append(deepcopy(msg[-1]))
+        conv.message = deepcopy(req["messages"])
         e, dia = DialogService.get_by_id(conv.dialog_id)
         if not e:
             return get_data_error_result(retmsg="Dialog not found!")