[8.15](backport #41077) [Heartbeat] Add managed status reporter at monitor factory level

[mergify]

Proposed commit message

Add status reporting for monitors when running under elastic-agent, this will allow the Fleet UI to reflect theres an issue with one or more heartbeat integrations.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

1. Build agentbeat locally with:

 DEV=true SNAPSHOT=true  PLATFORMS=linux/amd64 mage package

2. Build elastic-agent locally with:

DEV=true SNAPSHOT=true PLATFORMS=linux/amd64 PACKAGES=docker mage package

3. Enroll a non-complete elastic-agent into a private location policy with a browser monitor assigned.
4. Check agent status is eventually reported as degraded and the integration marked as failed.

   ---

   This is an automatic backport of pull request [Heartbeat] Add managed status reporter at monitor factory level #41077 done by Mergify.

[elasticmachine]

Pinging @elastic/obs-ds-hosted-services (Team:obs-ds-hosted-services)

[emilioalvap]

Closing due to parent PR introducing linting issues, will follow with a manual backport after ##41128 is merged.