Subclass chat messages from Document (#86)

knowledgehub/chatbot/base.py

@@ -1,9 +1,10 @@
 from abc import abstractmethod
 from typing import List, Optional
 
-from langchain.schema.messages import AIMessage, SystemMessage
 from theflow import SessionFunction
 
+from kotaemon.base.schema import AIMessage, SystemMessage
+
 from ..base import BaseComponent
 from ..base.schema import LLMInterface
 from ..llms.chats.base import BaseMessage, HumanMessage