[REQUEST]: Update documentation for fleet-managed agents that run inside a container (docker, k8s, etc.)

[pkoutsovasilis]

Description

Description

With the recent changes introduced in this PR, the behavior of Fleet-managed Elastic Agent running in a container has been updated to improve enrollment handling. These changes impact how an agent responds to being unenrolled from the Fleet UI, requiring documentation updates to clarify expected behavior for users.

Key Behavior Changes only for Elastic Agent running inside a container:

• Enrollment Verification: The agent now checks stored enrollment conditions and only re-enrolls when necessary.
• Unenrollment Handling: If an Elastic Agent is unenrolled through the Fleet UI but still has a valid enrollment token provided via environment variables, the next container restart will cause it to re-enroll automatically.
• Previously (Older Versions): Unenrolled agents would remain unenrolled and not re-enroll, even if a valid enrollment token was still available.

Resources

PR: elastic/elastic-agent#6568
Issue: elastic/elastic-agent#3586

Collaboration

The documentation team will investigate the issue and create the initial content.

Point of contact.

Main contact: @pkoutsovasilis

Stakeholders: @nimarezainia @cmacknz

[kilfoyle]

Thanks @pkoutsovasilis for the details! The docs are currently frozen while we migrate to a new system, but I'll be able to look after this after they open up again toward the end of February or early March.