Fix metadata in get_list() (#12906)

### What problem does this PR solve?

test_update_document.py failed as metadata is not included in the
response of get_list(), fix the issue.

### Type of change

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

api/db/services/document_service.py

@@ -109,7 +109,12 @@ class DocumentService(CommonService):
 
         count = docs.count()
         docs = docs.paginate(page_number, items_per_page)
-        return list(docs.dicts()), count
+
+        docs_list = list(docs.dicts())
+        metadata_map = DocMetadataService.get_metadata_for_documents(None, kb_id)
+        for doc in docs_list:
+            doc["meta_fields"] = metadata_map.get(doc["id"], {})
+        return docs_list, count
 
     @classmethod
     @DB.connection_context()