SDK for session (#2354)

### What problem does this PR solve?

Includes SDK for creating, updating sessions, getting sessions, listing
sessions, and dialogues
#1102 
### Type of change

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

---------

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

sdk/python/ragflow/__init__.py

@@ -4,4 +4,5 @@ __version__ = importlib.metadata.version("ragflow")
 
 from .ragflow import RAGFlow
 from .modules.dataset import DataSet
-from .modules.chat_assistant import Assistant
+from .modules.assistant import Assistant
+from .modules.session import Session