[Fleet] Agent status alerts for monitoring

[karenzone]

Summary

Updates monitoring docs to encourage use of new Elastic Agent out-of-the-box alert rules.

Closes: elastic/ingest-docs#1873

PREVIEWS:

• https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4469/reference/fleet/agent-health-status#agent-health-status-outage
• https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4469/reference/fleet/monitor-elastic-agent#fleet-alerting

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

[github-actions]

✅ Vale Linting Results

No issues found on modified lines!

[github-actions]

🔍 Preview links for changed docs

• reference/fleet/agent-health-status.md
• reference/fleet/monitor-elastic-agent.md

[nimarezainia]

🔍 Preview links for changed docs

* [reference/fleet/agent-health-status.md](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4469/reference/fleet/agent-health-status)

* [reference/fleet/monitor-elastic-agent.md](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/4469/reference/fleet/monitor-elastic-agent)

@karenzone I'm not seeing what the changes are in these docs particularly the 2nd page listed here. I'll dig around a bit more but the agent status alerting has been changed significantly.

@nchaulet @MichelLosier I was wondering if you had a recording on how to use the new alerts?

[nchaulet]

@nchaulet @MichelLosier I was wondering if you had a recording on how to use the new alerts?

I recored this quick one for Karen sometime ago if it can help https://github.com/user-attachments/assets/2490f16d-4b1c-4d4b-9e95-3c745d0d0e6a

[nimarezainia]

@nchaulet @MichelLosier I was wondering if you had a recording on how to use the new alerts?

I recored this quick one for Karen sometime ago if it can help https://github.com/user-attachments/assets/2490f16d-4b1c-4d4b-9e95-3c745d0d0e6a

thank you. I think we need to dive a bit deeper into the agent unhealthy rule template in the docs. I'll play with that a bit more.