JiSoo Park

[Feature Request] Implements indexSettings similarity.

3

### Is your feature request related to a problem? Please describe Currently, there is no [similarity setting](https://opensearch.org/docs/latest/search-plugins/keyword-search/#similarity-algorithms) in [indexSettings](https://opensearch.org/docs/latest/install-and-configure/configuring-opensearch/index-settings/) when creating new index through CreateIndexRequest in opensearch. The Elasitcsearch java-client...

Add similarity settings when using CreateIndexRequest

1

### 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...