Fix bugs in agent api and update api document (#3996)

### What problem does this PR solve?

Fix bugs in agent api and update api document

### Type of change

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

@@ -29,7 +29,7 @@ class Session(Base):
                 raise Exception(json_data["message"])
             if line.startswith("data:"):
                 json_data = json.loads(line[5:])
-                if not json_data["data"]:
+                if json_data["data"] is not True:
                     answer = json_data["data"]["answer"]
                     reference = json_data["data"]["reference"]
                     temp_dict = {