Phoenix project to store all docker images used in CI

We need to control the images used in CI/CD so we can revert if a newer image breaks CI

• buildkit rootless image
• pixi image
• rattler-build + PhoenixCmake image
• debian base image
• pixi base image
• doxigen documentation, test tools are managed by pixi so we don't need special images
• CTest
• ...

Also keep back-up:

• Implement CI to automatically create/take these images from latest (on dockerhub, etc.) and store them in container registry of project
  • CI scheduler to do this every month?
    • renovate bot will propose an update whenever the base images can be updated, so we don't need a schedule to rebuild the images.
  • use crane to back-up previous image (keep 1-2 months old images)