Currently the metrics endpoint is part of the composer-api. The metrics endpoint should be separate from both the composer-api and the worker-api.

It needs a separate listener, and can run on an arbitrary port. The endpoint needs to be `/metrics` like before, and needs to be plain http. It is not intended to be exposed to the wider internet.

Changing this should happen in a staggered way, so that it doesn't break the current deployment:

1. Add the new listener/endpoint (make sure the update the container entrypoint file as well), but keep the current one in place
2. Make the necessary changes in app-interface to our servicemonitor: https://gitlab.cee.redhat.com/service/app-interface/-/blob/master/resources/observability/servicemonitors/image-builder.servicemonitor.yml . Make it scrape both endpoints.
3. Update our openshift templates https://github.com/osbuild/osbuild-composer/tree/main/templates with a new Service and container port for the new endpoint.
4. Once merged and up and running, remove the old endpoint from the service monitor so it stops scraping that one, and remove it from our templates; and remove the endpoint from the composer-api httpmux.