[DOC] Search latency stats for coordinator node

[sgup432]

What do you want to do?

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

Tell us about your request. Provide a summary of the request and all versions that are affected.
We added a feature as part of opensearch-project/OpenSearch#8386 where we now have the ability to track coordinator level search latency stats. We need to document this feature.
Note: This feature already went as part of 2.11 release.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
opensearch-project/OpenSearch#8386 - PR
opensearch-project/OpenSearch#8381 - Related issue

[hdhalter]

@sgup432 - Can you please take a stab at documenting this? If you put up a PR with the required information, we will review and merge. Thanks!