New internal API

/cc @ggillies @nicholasklick @ash2k

This is an FYI : In gitlab-org/gitlab!41045 (merged) we will be enabling a new internal API.

The plan is to test out the GitLab K8s agent on preprod first (gitlab-org/gitlab#227513 (closed)). But the internal API will be available by default.

In theory, this should have no impact. Simply do not setup gitlab-kas in environments that don't use it. :)

Note that in the event of a problem, we can still disable the feature flag :kubernetes_agent_internal_api.