Test: Added test cases for Create Session With Chat Assistant HTTP API (#6902)

### What problem does this PR solve?

cover [create session with chat
assistant](https://ragflow.io/docs/dev/http_api_reference#create-session-with-chat-assistant)
endpoints

### Type of change

- [x] add test cases

sdk/python/test/test_http_api/test_dataset_mangement/test_delete_datasets.py

@@ -117,6 +117,7 @@ class TestDatasetsDeletion:
         res = list_datasets(get_http_api_auth)
         assert len(res["data"]) == 0
 
+    @pytest.mark.slow
     def test_concurrent_deletion(self, get_http_api_auth):
         ids = batch_create_datasets(get_http_api_auth, 100)
 

sdk/python/test/test_http_api/test_dataset_mangement/test_list_datasets.py

@@ -337,6 +337,7 @@ class TestDatasetsList:
         else:
             assert res["message"] == expected_message
 
+    @pytest.mark.slow
     def test_concurrent_list(self, get_http_api_auth):
         with ThreadPoolExecutor(max_workers=5) as executor:
             futures = [executor.submit(list_datasets, get_http_api_auth) for i in range(100)]

sdk/python/test/test_http_api/test_dataset_mangement/test_update_dataset.py

@@ -236,6 +236,7 @@ class TestDatasetUpdate:
         res = update_dataset(get_http_api_auth, dataset_id, {"unknown_field": 0})
         assert res["code"] == 100
 
+    @pytest.mark.slow
     def test_concurrent_update(self, get_http_api_auth, add_dataset_func):
         dataset_id = add_dataset_func