[DOC] ML Inference Search Request Processor and ML Inference Search Response Processor

[mingshl]

What do you want to do?

• Request a change to existing documentation
• [ x] Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request.
add new documentation for ML Inference Search Request Processor and ML Inference Search Response Processor
*Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
2.16
What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
opensearch-project/ml-commons#2173