Add sdk for list agents and sessions (#3848)

### What problem does this PR solve?

Add sdk for list agents and sessions

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

sdk/python/ragflow_sdk/modules/session.py

@@ -8,12 +8,12 @@ class Session(Base):
         self.id = None
         self.name = "New session"
         self.messages = [{"role": "assistant", "content": "Hi! I am your assistant，can I help you?"}]
-        self.chat_id = None
-        self.agent_id = None
         for key,value in res_dict.items():
             if key =="chat_id" and value is not None:
+                self.chat_id = None
                 self.__session_type = "chat"
             if key == "agent_id" and value is not None:
+                self.agent_id = None
                 self.__session_type = "agent"
         super().__init__(rag, res_dict)