Pull Commodore image from ghcr.io

[BacLuc]

As per decision here: https://kb.vshn.ch/corp-tech/decisions/container-image-location.html#_decision

• The PR has a meaningful title. It will be used to auto-generate the
  changelog.
  The PR has a meaningful description that sums up the change. It will be
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• PR contains a single logical change (to build a better changelog).
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[simu]

LGTM. I have no real opinion either way. We almost never have issues with pulling the Commodore image from docker.io (since we have the OSS pull rate limit exemption for docker.io/projectsyn).

[BacLuc]

Lets see if there pile up more issues with pulling from docker.io.