Test: Added test cases for Delete Documents HTTP API (#6175)

### What problem does this PR solve?

cover [delete
documents](https://ragflow.io/docs/dev/http_api_reference#delete-documents)
endpoints

### Type of change

- [x] add test cases

sdk/python/test/test_http_api/common.py

@@ -150,3 +150,9 @@ def update_documnet(auth, dataset_id, document_id, payload):
     url = f"{HOST_ADDRESS}{FILE_API_URL}/{document_id}".format(dataset_id=dataset_id)
     res = requests.put(url=url, headers=HEADERS, auth=auth, json=payload)
     return res.json()
+
+
+def delete_documnet(auth, dataset_id, payload=None):
+    url = f"{HOST_ADDRESS}{FILE_API_URL}".format(dataset_id=dataset_id)
+    res = requests.delete(url=url, headers=HEADERS, auth=auth, json=payload)
+    return res.json()