[DOC] Add document for top n queries by CPU and Memory

[ansjcy]

What do you want to do?

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

We are introducing top n queries by CPU and Memory with
opensearch-project/OpenSearch#13172
opensearch-project/OpenSearch#13739

Need to update the existing document to reflect that: https://opensearch.org/docs/latest/observing-your-data/query-insights/top-n-queries/

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.