Fix docs

[nsano-rururu]

Description

Checklist

• I have reviewed the contributing guidelines.
• I have included unit tests for my changes or additions.
• I have successfully run make test-docker with my changes.
• I have manually tested all relevant modes of the change in this PR.
• I have updated the documentation.
• I have updated the changelog.

Questions or Comments

[Copilot]

Pull request overview

This PR updates the documentation to reflect accurate alerter names and current URLs. The changes improve consistency between the alerter list in elastalert.rst and the detailed alerter sections in alerts.rst.

• Updates alerter names to match their actual implementations (e.g., "Line Notify" → "LINE Messaging API", "Grafana OnCall" → "Grafana IRM")
• Updates URLs to point to current documentation (Alertmanager and Grafana IRM)
• Adds consistent line numbering and removes trailing whitespace

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
docs/source/elastalert.rst	Updates alerter list with corrected names (Grafana IRM, IRIS, LINE Messaging API, Webex Webhook, YZJ) and improves formatting with consistent line numbering
docs/source/alerts.rst	Updates section titles and URLs for Alertmanager and Grafana IRM alerters to point to current documentation

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