Test: Add web API test suite for knowledge base operations (#8254)

### What problem does this PR solve?

- Implement RAGFlowWebApiAuth class for web API authentication
- Add comprehensive test cases for KB CRUD operations
- Set up common fixtures and utilities in conftest.py
- Add helper functions in common.py for web API requests

The changes establish a complete testing framework for knowledge base
management via web API endpoints.

### Type of change

- [x] Add test case

test/testcases/test_web_api/test_kb_app/conftest.py

@@ -0,0 +1,38 @@
+#
+#  Copyright 2025 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+import pytest
+from common import batch_create_datasets
+from libs.auth import RAGFlowWebApiAuth
+from pytest import FixtureRequest
+from ragflow_sdk import RAGFlow
+
+
+@pytest.fixture(scope="class")
+def add_datasets(request: FixtureRequest, client: RAGFlow, WebApiAuth: RAGFlowWebApiAuth) -> list[str]:
+    def cleanup():
+        client.delete_datasets(ids=None)
+
+    request.addfinalizer(cleanup)
+    return batch_create_datasets(WebApiAuth, 5)
+
+
+@pytest.fixture(scope="function")
+def add_datasets_func(request: FixtureRequest, client: RAGFlow, WebApiAuth: RAGFlowWebApiAuth) -> list[str]:
+    def cleanup():
+        client.delete_datasets(ids=None)
+
+    request.addfinalizer(cleanup)
+    return batch_create_datasets(WebApiAuth, 3)