Avoid Docker registry pull rate limit errors

It occurs with GitLab runners that use Docker executor.

Solutions in my mind:

• Use mirror.gcr.io
  • Source: https://jeffmaury.hashnode.dev/get-rid-of-docker-hub-limits-with-podman
• Use a local mirror at the GitLab runner instance
• Use Salsa registry
  • By that I mean storing the container images that we pull from Docker registry somewhere at the Salsa registry, update them frequently and pull from this place instead of DockerHub.
  • Inspired by: https://github.com/docker-mirror/images

We may implement/document multiple solutions for this problem.