fix: OpenSearch async client initialization

[Nitro963]

Proposed Changes:

In async environment _ensure_initialized sync method is being called on the main thread, and as it may take time depending on network it will cause the entire event loop to block and the application will freeze until all retries finished if any.

How did you test it?

Manual testing within FastAPI async server

[CLAassistant]

All committers have signed the CLA.

[davidsbatista]

Thanks for your proposal @Nitro963

This makes sense, but I would rather do it differently, since this might introduce lots of overhead each time an operation is performed.

Ideally, creating a async def _ensure_initialized_async(self) check how it's done for the Chroma document store.

[Nitro963]

@davidsbatista I've updated implementation with a new initialization method

[davidsbatista]

thanks @Nitro963 LGTM

[davidsbatista]

LGTM!