add doc for alert insight agent

[yuye-aws]

Description

Add doc for alert insight agent

Issues Resolved

Add doc for alert insight agent

Checklist

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[github-actions]

Thank you for submitting your PR. The PR states are In progress (or Draft) -> Tech review -> Doc review -> Editorial review -> Merged.

Before you submit your PR for doc review, make sure the content is technically accurate. If you need help finding a tech reviewer, tag a maintainer.

When you're ready for doc review, tag the assignee of this PR. The doc reviewer may push edits to the PR directly or leave comments and editorial suggestions for you to address (let us know in a comment if you have a preference). The doc reviewer will arrange for an editorial review.

[qianheng-aws]

Need to add verification on insight API as well. You can see its API definition here: https://github.com/opensearch-project/dashboards-assistant/blob/50fef5c06993b110367314400f857042ef646568/server/routes/summary_routes.ts#L83, and write related test like summary API.

[yuye-aws]

Need to add verification on insight API as well. You can see its API definition here: https://github.com/opensearch-project/dashboards-assistant/blob/50fef5c06993b110367314400f857042ef646568/server/routes/summary_routes.ts#L83, and write related test like summary API.

Ack. Updated.

[yuye-aws]

Pinging @ruanyl for CI check and merge.