Create sample .gitlab-ci.yml to exercise the runner with supported base images

[pauldoomgov]

As a GitLab Runner for cloud.gov developer, I would like a standard .gitlab-ci.yml template that exercises the runner with a list of common base images, So I may expand support and prevent regressions.

The specifics of how we launch app instances and layer items on top to support GitLab Runner Helper are brittle and incomplete. We need something to validate against.

Acceptance Criteria

• [ ] Sample .gilab-ci.yml in this project
• [ ] Evidence of use of the sample in a test GitLab repo

[pauldoomgov]

The specific list can evolve over time. Consider items under https://hub.docker.com/search?image_filter=official&operating_system=linux&architecture=amd64&categories=Operating%20Systems including:

• busybox
• alpine
• ubuntu
• debian
• amazonlinux

Plus these "not official" images:

• redhat/ubi8
• redhat/ubi9

x86_64 targets for all.