[9.0] (backport #10060) fix: take into account units state on liveness

[mergify]

What does this PR do?

This PR adds the check of the component's unit's state on liveness endpoint. If a component state is healthy, but a unit state is degraded or failed, the liveness endpoint will return a 500.

Checklist

• I have read and understood the pull request guidelines of this project.
• 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/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

Liveness probes will now fail if a component state is healthy but any of the units is failed or degraded, likely causing the container to be restarted (see https://kubernetes.io/docs/concepts/configuration/liveness-readiness-startup-probes/#liveness-probe).

Related issues

• Closes [monitoring] /liveness?failon=degraded not returning HTTP 500 #8047

---

This is an automatic backport of pull request #10060 done by [Mergify](https://mergify.com).

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[rubenruizdegauna]

LGTM

[elastic-sonarqube]

Quality Gate passed

Issues
1 New issue
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: b56972a

Failed CI Steps

• arm:sudo: upgrade

History

• 💛 Build #27310 was flaky 78b49ec

cc @rubenruizdegauna