Add git to the shell builder image

Related to gitlab-org/gitlab-shell#173 (closed)

And directly needed as a result of: gitlab-org/gitlab-shell!350 (merged)

This is because the go modules are not longer stored in git as vendored, and we instead fetch them using go install.

Use the artifacts method of passing the containers

• For the UBI image, the builder images are properly broke out for shell, so we can just add git as an additional one
• For the regular images, the builder images are not properly handled yet, shell had all of the go image, now it has all of the git image (which is based on the go image for non-ubi containers). This is just the minimal change to fix the broken master.