Publish to `ghcr.io`, the GitHub Container Registry

[felipecrs]

This is especially important since Docker Hub has imposed pull rate limits.

This way we could also use the deno images with:

$ docker run ghcr.io/denoland/deno

Reference: https://github.com/docker/build-push-action/blob/master/docs/advanced/push-multi-registries.md

[UltiRequiem]

I think we can close this? https://github.com/orgs/denoland/packages?repo_name=deno_docker

[felipecrs]

There is only a very old alpine based image there.