Use Distroless docker images for `.gitlab-ci.yml` templates

Problem to solve

Deployed Docker images should be as small as possible so they:

1. load quickly
2. take up less storage
3. have less security surface area

Intended users

Further details

CI/CD templates use fat base images that include a lot of functionality that isn't actually needed by the resulting app. Alpine is a great base image that is smaller, but Google's Distroless images are even thinner.

Proposal

Permissions and Security

Documentation

What does success look like, and how can we measure that?

Links / references