Remove Cilium Alert functionality from GitLab Rails and GitLab Agent for Kubernetes

Why are we doing this work

Container Network Security and Container Host Security have been deprecated and will be removed in %15.0. As part of this removal, we will be removing the Cilium Alert functionality from the GitLab Agent (first implemented in gitlab-org/cluster-integration/gitlab-agent!211 (merged)), as well as the associated Rails backend code (internal API endpoint + services).

Relevant links

Non-functional requirements

• Documentation:
• Feature flag:
• Performance:
• Testing:

Implementation plan

• backend Remove the cilium_alert agent module
• backend Remove the /cilium_alert internal API endpoint and the NetworkAlertService
• backend Remove accompanying test suites
• documentation Remove the GitLab Agent alert metrics section from the Internal API docs