fix(milvus): use explicit output_fields in query_vector for milvus-lite 3.0 compatibility (backport #6091) (#6096)

## Summary
- `query_vector` used `output_fields=["*"]` in `client.search()`, but
milvus-lite 3.0 no longer expands `["*"]` to include JSON fields in
search results, causing `KeyError: 'chunk_content'`
- Changed to `output_fields=["chunk_content"]`, consistent with
`query_keyword` and `query_hybrid` which already use explicit field
names
- The `remote::milvus` provider (connecting to a full Milvus server) was
not affected

Closes #6090
RHAIENG-5601

## Test plan
- [x] Reproduced the bug with milvus-lite 3.0 via standalone script
- [x] Reproduced via REST API (`/v1/vector-io/query` returns 500,
`/v1/vector_stores/{id}/search` returns empty)
- [x] Verified fix works with milvus-lite 3.0 - both endpoints return
correct results
- [x] Fix is backward compatible with milvus-lite 2.x (explicit field
names work in both versions)<hr>This is an automatic backport of pull
request #6091 done by [Mergify](https://mergify.com).

Signed-off-by: Derek Higgins <derekh@redhat.com>
Co-authored-by: Derek Higgins <derekh@redhat.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

src/ogx/providers/remote/vector_io/milvus/milvus.py

@@ -238,7 +238,7 @@ async def query_vector(
             "data": [embedding],
             "anns_field": "vector",
             "limit": k,
-            "output_fields": ["*"],
+            "output_fields": ["chunk_content"],
         }
 
         # Only apply radius threshold if score_threshold is meaningful