Use ghcr.io by default instead of docker hub

[nvuillam]

Planned for v9

[bdovaz]

Any reason / motivation?

[nvuillam]

@bdovaz enforced docker hub rate limits since 2025 :)

https://docs.docker.com/docker-hub/usage/

https://about.gitlab.com/blog/2025/03/24/prepare-now-docker-hub-rate-limits-will-impact-gitlab-ci-cd/

[github-actions]

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