Add documentation for ml inference search request processor/ search response processor

[mingshl]

Description

add documentation for ml inference search request processor and ml inference search response processor.

Issues Resolved

Closes https://github.com/opensearch-project/documentation-website/issues/7792

Version

2.16

Frontend features

If you're submitting documentation for an OpenSearch Dashboards feature, add a video that shows how a user will interact with the UI step by step. A voiceover is optional.

Checklist

• [ ] 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.

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[mingshl]

PR under draft

[hdhalter]

PR under draft

Thanks so much, @mingshl! I added the label 'in progress', so feel free to continue to work on it until it is ready for review. At that point, feel free to tag any tech reviewers, or tag me if ready for doc review.

[mingshl]

@hdhalter ready for review