[FEATURE] Lucene Based k-NN search support

[vamshin]

Is your feature request related to a problem?
Recently Lucene started building in-house Approximate k-NN search in Java based on HNSW algorithm. k-NN plugin already has support for HNSW based out of C library namely NMSlib. By having the Lucene based HNSW support, we will be able to provide AKNN functionality independently outside of k-NN plugin with out having to rely on the NMSlib or FAISS. This will unlock the platform dependency issues because of C based libraries.

As a prerequisite we need to introduce new data type dense_vector in OpenSearch core and build Field Mappers to index data from this field to Lucene graphs.

[elfisher]

I added the roadmap label since this is on the project roadmap.

[alexahorgan]

Demo feedback (8/3/22):

Outcome:
Approved, ship it.

Action Items/Follow up:

• Connect with documentation team to document limits and approaches.
• Follow up on performance and scale.
• Begin exploring opportunities to leverage UI to drive insights/run searches.