fix doc for alert summary and insight

[yuye-aws]

Description

1. Correct the API call to create alert summary agents
2. Assign url with templates from flow framework

Issues Resolved

List any issues this PR will resolve, e.g. Closes [...].

Checklist

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[yuye-aws]

https://github.com/opensearch-project/flow-framework/blob/2.x/sample-templates/alert-summary-log-pattern-agent.json This file is not ready yet. I'm creating a PR towards the flow framework repo.