GitLab Kubernetes Agent's usage metrics rejected

When kas sends usage metrics it can only provide Gitlab-Kas-Api-Request header for authentication, it's not authenticating as an agent. This is because it's making the request on it's own behalf and not on behalf of some particular agent. In fact, 0 may be connected at the time the request is made. But server-side code expects the agent token to be present in the Authorization header. This makes the request fail with 403.