workflow: Clean up docker images for closed PRs

[mircea-pavel-anton]

References

• https://github.com/fluent/fluent-bit/blob/master/.github/workflows/pr-closed-docker.yaml
• https://github.com/bjw-s/container-images/blob/main/.github/workflows/scheduled-cleanup.yaml
• https://github.com/immich-app/immich/blob/main/.github/workflows/docker-cleanup.yml

Downstream repos blocked by this:

• [x] https://github.com/mirceanton/talswitcher/issues/9
• [x] https://github.com/mirceanton/kube-switcher/issues/20
• [x] https://github.com/mirceanton/external-dns-provider-mikrotik/issues/69
• [x] https://github.com/mirceanton/home-ops/issues/367

[mircea-pavel-anton]

https://github.com/immich-app/immich/blob/main/.github/workflows/docker-cleanup.yml

[mircea-pavel-anton]

fixed in af4187e0d9f6b207e5814b61c78f2bf131fdc1b6