Add similarity settings when using CreateIndexRequest

[ritty27]

Description

This PR Partial resolution https://github.com/opensearch-project/opensearch-java/issues/987 There are several types of Similarity, so I only made some of the representative ones (BM25, Boolean). Therefore, the code does not implement all similarity(DFI, DFR, IB etc.). If the this commit is okay, I will try to implement other types similarly.

Issues Resolved

#987

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[dblock]

Looks good to me, needs tests, documentation, samples, etc.

Take a look at https://github.com/opensearch-project/opensearch-api-specification too. I think we want to derive a lot of this code from spec (@Xtansia is working on a generator #366).

[Xtansia]

An iteration of index settings similarity was generated and released as part of v3.0.0. Any future changes/fixes should be addressed in the https://github.com/opensearch-project/opensearch-api-specification