[DOCS] "Unhealthy" Agent status and integration policy errors

[joepeeples]

Description

Per https://github.com/elastic/security-team/issues/3494, integration policy errors and status are now provided to help troubleshoot when an Elastic Agent has an "unhealthy" status.

There are currently three main causes of unhealthy status caused by Endpoint; error messages will identify these, and will most likely resolve the status once the user resolves these:

• macOS system extension
• macOS Full Disk Access
• Linux potential deadlock

Notes

• Review Fleet docs on Agent status, and determine if we need to collaborate on any content
• Coincides with [DOCS] Add Endpoint troubleshooting document: Linux deadlock #2197 (Linux potential deadlock)

Example