Smaller container images for review app jobs

TL;DR

This MR will give users 70 seconds back per MR when deploying a review-app 🎉

Context

Closes #386783 (closed)

About review-apps deployment

• The review-deploy job is the job deploying review-apps to the k8s cluster.
• review-build-cng-env needs to be finished before the review-deploy job run (i.e. it's on the critical path)

If we improve the time it takes to run one of those two jobs, users will have a faster feedback.

review-build-cng-env job

review-build-cng-env takes around 30 seconds to setup a runner, mainly because the container image it is downloading is big (~370MB or 1GB to download - I don't know which value is used):

REPOSITORY                                                                    TAG          IMAGE ID        CREATED         PLATFORM    SIZE          BLOB SIZE
registry.gitlab.com/gitlab-org/gitlab-build-images/debian-bullseye-ruby-2.7   bundler-2.3  0391eef3ffaa    5 days ago      linux/amd64 1019.2 MiB    362.9 MiB

review-deploy job

review-deploy takes around 55 seconds to setup a runner, mainly because the container image it is downloading is very big (~581MB or 2GB to download - I don't know which value is used):

REPOSITORY                                                   TAG                              IMAGE ID        CREATED         PLATFORM    SIZE          BLOB SIZE
registry.gitlab.com/gitlab-org/gitlab-build-images/ruby-3.0  gcloud-383-kubectl-1.23-helm-3.5 add63212b0c8    7 weeks ago     linux/amd64       1.9 GiB       581.8 MiB

What does this MR do?

Experiment with smaller container images to improve the time it takes to setup a runner:

• For review-build-cng-env, we use a ruby-alpine image (e.g. ruby:2.7-alpine), as we only run one ruby script in the entire job (e.g. https://gitlab.com/gitlab-org/gitlab/-/jobs/3548098581)
• For review-deploy, we use an image with only helm/kubectl installed: dtzar/helm-kubectl. The other image we used has gcloud baked in (huge dependency), but we do not use it in this job (e.g. https://gitlab.com/gitlab-org/gitlab/-/jobs/3552387169)

Results

• When the cache was cold, review-build-cng-env took 11 seconds to setup a runner (https://gitlab.com/gitlab-org/gitlab/-/jobs/3553231360#L6)
  • 20 seconds improvement 🚀
• When the cache was cold, review-deploy took 11 seconds to setup a runner (https://gitlab.com/gitlab-org/gitlab/-/jobs/3553231370).
  • 50 seconds improvement 🚀

What's next?

Those jobs will be made faster if we can avoid a git clone in them. This will be tried out as part of #191273 (closed) (see #191273 (comment 1227409061) for context).

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.