Add support of KNN queries

[manosetro]

Since version 8.4 of the elasticsearch-java client, KnnQuery implements only JsonpSerializable.

Before that change it was defined as:
public class KnnQuery extends QueryBase implements QueryVariant

As a result, the KnnQuery cannot be used in the NativeQuery class.

[sothawo]

That's not an issue of Spring Data Elasticsearch but of Elasticsearch, you might want to a open an issue in their repository.

[manosetro]

The issue here is that the change in elasticsearch-java has been made to conform to the underlying API's specs.

The knn option is now part of the request body of the _search endpoint. Similarly to docvalue_fields, point in time (PIT), etc.

I cannot find how the knn option can be send in the _search request in the current version of Spring-Data-Elasticsearch.
I suppose that the way to support KnnQuery is to add a .withKnnQuery method in the NativeQuery class.

Did I miss anything?

[sothawo]

Ok, that would needed to be added to the NativeQuery, the builder and then be used when buildig the actual Elasticsearch client searchquery.