Add a slim ruby image for gitlab
Context
https://gitlab.com/gitlab-org/gitlab/-/jobs/4830787468#L6 took 52 seconds to download the default container image.
I'd like to have an image for "ruby-only jobs" that will be smaller to download when the runner needs to download the image from the registry.
I hope that the resulting image in this MR will be fairly small to download. If that's not the case, we can close this MR.
What does this MR do and why?
Adds a container image for gitlab-org/gitlab
pipelines with ruby and debian-slim.
This container image is meant to be used for jobs that have to install ruby gems, sometimes from source, so they need the adequate OS dependencies installed (installed via https://gitlab.com/gitlab-org/gitlab-build-images/-/blob/master/Dockerfile.custom#L16).
They also need a small-ish image, so that the job can download the image faster than the regular image.
Results
Job: https://gitlab.com/gitlab-org/gitlab-build-images/-/jobs/4875094881:
- We indeed install the OS dependencies in https://gitlab.com/gitlab-org/gitlab-build-images/-/jobs/4875094881#L72
Checklist
-
(If applicable) Add patches if required for upgrading Ruby version in https://gitlab.com/gitlab-org/gitlab-build-images/-/tree/master/patches/ruby.