Bug fix: OpenSearch chunk update some api error (#9032)

### What problem does this PR solve?

Fix a small non-blocking main workflow bug about chunk update When
OpenSearch is the doc engine.
When you wanna enable/disable a chunk in the web-page “Knowledge Base /
Dataset / Chunk”, the bug ocurred.
<img width="2388" height="662" alt="image"
src="https://github.com/user-attachments/assets/575987a0-c929-4589-bfa0-ba54e137cfd9"
/>

The reaseon why it ocurred is that some api params between OpenSearch
and ES differs. It functioned well no matter enable/disable/rewrite the
chunk after I fixed. I also checked the result when using the chat
web-page.

<img width="2394" height="660" alt="image"
src="https://github.com/user-attachments/assets/8b899dc6-d769-4e80-8dd8-ad0fbbca5f78"
/>

I will still focus on vector-database espeically OpenSearch.

### Type of change

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

Co-authored-by: 张雨豪 <zhangyh80@chinatelecom.cn>
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

rag/utils/opensearch_conn.py

@@ -329,7 +329,7 @@ class OSConnection(DocStoreConnection):
             chunkId = condition["id"]
             for i in range(ATTEMPT_TIME):
                 try:
-                    self.os.update(index=indexName, id=chunkId, body=doc)
+                    self.os.update(index=indexName, id=chunkId, body={"doc":doc})
                     return True
                 except Exception as e:
                     logger.exception(