Support fetching bundled gems from a Docker image
This fetches an image of the gems bundle when FETCH_GEMS_BUNDLE_IMAGE == 'true' (this variable is only set in the CNG-mirror project).
The image itself is built in a new build-gems-bundle-image job in the gitlab pipelines, this is done in gitlab-org/gitlab!19402 (closed).
Edited by Rémy Coutable