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:

• ci: cleanup docker images after a PR is closed talswitcher#9
• ci: cleanup docker images after a PR is closed kube-switcher#20
• ci: Cleanup Docker images after PR gets closed external-dns-provider-mikrotik#69
• ci: Cleanup Docker images after PR gets closed home-ops#367

[mircea-pavel-anton]

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

[mircea-pavel-anton]

fixed in af4187e