[DOC] Update score formula for cosine similarity in KNN Search

[VijayanB]

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• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
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Tell us about your request. Provide a summary of the request.

Update following

1. Now, lucene, nmslib and faiss use same OpenSearch Score and distance function for cosine similarity.
2. KNN Script score also supports same score as KNN Aprox search

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
2.19

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
opensearch-project/k-NN#2375