Add the public-image-archive project to projects.yml

Why is this change being made?

New project added to https://gitlab.com/gitlab-org/public-image-archive for providing customers who can't use dockerhub with our omnibus gitlab images. For now we are uploading specific images for customers as they request them, and typically older images. Hence the -archive in the name.

In the future we will likely automate this for new releases: gitlab-org/omnibus-gitlab#7459 and at that time we may spend more time coming up with a new project name.

Initially targeting the omnibus docker images, so the active omnibus maintainers have been added as maintainers in this project.

Author Checklist

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