This container can be pulled via:
  docker pull registry.opensuse.org/filesystems/ceph/pacific/images/ceph/prometheus-alertmanager:0.16.2
  docker pull registry.opensuse.org/filesystems/ceph/pacific/images/ceph/prometheus-alertmanager:0.16.2.10.132
  docker pull registry.opensuse.org/filesystems/ceph/pacific/images/ceph/prometheus-alertmanager:latest
  docker pull registry.opensuse.org/filesystems/ceph/pacific/images/ceph/prometheus-alertmanager:leap15.3

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.