Consider an container image mirror on Harvester

[meysholdt]

Is your feature request related to a problem? Please describe

• we got bitten by the docker.io rate limit today. Find a partial workaround here: .werft/vm/manifests: Replace docker.io with quay.io #8723
• image pulls could be faster. It needs to be evaluated though if this is due to IO performance on the VMs, network, or registry servers.

Describe the behavior you'd like

Fast image pulls without rate limit.

Depending on feasibility this could be a public image registry (e.g. https://cloud.google.com/container-registry/docs/pulling-cached-images, if that's accessible) or a registry in Harvester.

Describe alternatives you've considered

Additional context

[meysholdt]

This should be a pull-through docker registry.

Potentially this solution: https://docs.docker.com/registry/recipes/mirror/

[meysholdt]

Fixed via #9671: use a Docker Hub account instead of installing/maintaining our own image registry.