Despite return_embedding=False SearchEngineDocumentStore.query retrieves embedding_field

[tstadel]

Describe the bug
If we set return_embedding=False SearchEngineDocumentStore.query still requests all fields and does not exclude the embedding field. This slows down sparse retrieval if the index has embeddings as all embedding vectors unnecessarily go over the wire.

Expected behavior
SearchEngineDocumentStore requests embeddings only when needed.

Additional context
For batched queries this can reduce latency by 9%.

To Reproduce

1. create index with embeddings using OpenSearchDocumentStore
2. set return_embedding=False
3. run logging.getLogger("opensearch").setLevel(logging.DEBUG)
4. run document_store.query
5. see embeddings in response

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