Reciprocal Rank Fusion (RRF) normalization technique in hybrid query

[Johnsonisaacn]

Description

Adding ability to process and combine scores from multiple subqueries in neural search using the reciprocal rank fusion (RRF) technique. Built with a new processor and processor factory class apart from NormalizationProcessor. Changes to API included in RFC. Does not currently support weights when combining processed subquery scores, based on lack of examples in existing literature.

Related Issues

Resolves #[Issue number to be closed when this PR is merged] https://github.com/opensearch-project/neural-search/issues/865 https://github.com/opensearch-project/neural-search/issues/659

Check List

• [ ] New functionality includes testing.
• [ ] New functionality has been documented.
• [ ] API changes companion pull request created.
• [ ] Commits are signed per the DCO using --signoff.
• [ ] Public documentation issue/PR created.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.