Experiments with the Github Container Registry

Just trying things out here, the images are based on alpine. Meow! :smile_cat:

What the build.yaml workflow and scripts here are supposed to do:

• Build and test a container image using Actions

• Choose suitable tags for the image (see tag-from-ref.py)

• Scan the image for vulnerabilities using Trivy. The scan also runs regularly for the beta and latest tags in the scan_images.yaml workflow.

• If the image should be tagged, do that and push to GHCR.

If you run the resulting image it'll meow at you, you can even give a number of meows on the command line! :smiley_cat:

Cleaning old images

Building and pushing an image tagged beta for each commit accumulates old, now untagged beta images pretty quickly. The ghcr-prune.py script uses the GitHub packages API to list image versions, and optionally prunes untagged ones older than a given number of days. :broom:

The prune_images.yaml workflow uses this script to clean up once per month.