Use Distroless docker images for `.gitlab-ci.yml` templates
Problem to solve
Deployed Docker images should be as small as possible so they:
- load quickly
- take up less storage
- have less security surface area
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.