Adding retrieve specific fields docs

[AntonEliatra]

Description

Adding documentation for Retrieval of specific fields

Issues Resolved

Part of https://github.com/opensearch-project/documentation-website/issues/4785

Version

all

Checklist

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

[hdhalter]

@rishabhmaurya , can you please do a tech review? Thank you.

[kolchfa-aws]

@AntonEliatra Could you also add this and the search shard routing to the table in the index page for searching data? https://opensearch.org/docs/latest/search-plugins/searching-data/index/