[FEATURE] Support for Appoximate k-NN search

[lucebert]

Is your feature request related to a problem?

I am currently using the official OpenSearch Java SDK for my project, and I realized that it does not support the Approximate k-NN search feature.

What solution would you like?

I would like the Java SDK to provide support for the Approximate k-NN search. This would enable me to perform k-NN operations directly from the SDK without having to make raw API calls or use other workarounds.

What alternatives have you considered?

I have considered using raw API calls as a workaround, but it would be much more efficient and cleaner to have this functionality built directly into the SDK.

Do you have any additional context?

Please refer to the official OpenSearch documentation on Approximate k-NN search for more information on this feature.

[dblock]

I think you mean opensearch-java, moving this to that project. Then I think the client does actually support ANN, see #584 and #539. What's missing?

[lucebert]

Indeed, I was reviewing both projects and mistakenly intended to address this issue in the opensearch-sdk-java. My apologies. I might consider transitioning to opensearch-java.