This container can be pulled via:
  docker pull registry.opensuse.org/opensuse/alertmanager:0.28
  docker pull registry.opensuse.org/opensuse/alertmanager:0.28.0
  docker pull registry.opensuse.org/opensuse/alertmanager:0.28.0-27.7
  docker pull registry.opensuse.org/opensuse/alertmanager:latest

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.