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/test/test_sdk_api/t_agent.py

@@ -0,0 +1,9 @@
+from ragflow_sdk import RAGFlow,Agent
+from common import HOST_ADDRESS
+import pytest
+
+@pytest.mark.skip(reason="")
+def test_list_agents_with_success(get_api_key_fixture):
+    API_KEY=get_api_key_fixture
+    rag = RAGFlow(API_KEY,HOST_ADDRESS)
+    rag.list_agents()