build: push docker image to ghcr.io

[Thunderbottom]

With the new recent changes in dockerhub1, we should start pushing images to ghcr, and eventually phase out the existing dockerhub setup.

This PR adds a few configuration steps required to push images to ghcr alongside dockerhub.

[knadh]

Thanks @Thunderbottom. Have you been able to test/simulate this on another repo?

[Thunderbottom]

yes, I did simulate a dry-run of GH actions in this PR locally using act

Here's the output:

*DRYRUN* [goreleaser/goreleaser] 🚀  Start image=catthehacker/ubuntu:act-latest
*DRYRUN* [goreleaser/goreleaser]   🐳  docker pull image=catthehacker/ubuntu:act-latest platform= username= forcePull=false
*DRYRUN* [goreleaser/goreleaser]   🐳  docker create image=catthehacker/ubuntu:act-latest platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
*DRYRUN* [goreleaser/goreleaser]   🐳  docker run image=catthehacker/ubuntu:act-latest platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
*DRYRUN* [goreleaser/goreleaser]   ☁  git clone 'https://github.com/actions/setup-go' # ref=v2
*DRYRUN* [goreleaser/goreleaser]   ☁  git clone 'https://github.com/docker/login-action' # ref=v1
*DRYRUN* [goreleaser/goreleaser]   ☁  git clone 'https://github.com/docker/login-action' # ref=v2
*DRYRUN* [goreleaser/goreleaser]   ☁  git clone 'https://github.com/goreleaser/goreleaser-action' # ref=v2
*DRYRUN* [goreleaser/goreleaser] ⭐ Run Main Checkout
*DRYRUN* [goreleaser/goreleaser]   ✅  Success - Main Checkout
*DRYRUN* [goreleaser/goreleaser] ⭐ Run Main Set up Go
*DRYRUN* [goreleaser/goreleaser]   ✅  Success - Main Set up Go
*DRYRUN* [goreleaser/goreleaser] ⭐ Run Main Login to Docker Registry
*DRYRUN* [goreleaser/goreleaser]   ✅  Success - Main Login to Docker Registry
*DRYRUN* [goreleaser/goreleaser] ⭐ Run Main Login to GitHub Docker Registry
*DRYRUN* [goreleaser/goreleaser]   ✅  Success - Main Login to GitHub Docker Registry
*DRYRUN* [goreleaser/goreleaser] ⭐ Run Main Prepare Dependencies
*DRYRUN* [goreleaser/goreleaser]   ✅  Success - Main Prepare Dependencies
*DRYRUN* [goreleaser/goreleaser] ⭐ Run Main Run GoReleaser
*DRYRUN* [goreleaser/goreleaser]   ✅  Success - Main Run GoReleaser
*DRYRUN* [goreleaser/goreleaser] ⭐ Run Post Login to GitHub Docker Registry
*DRYRUN* [goreleaser/goreleaser]   ✅  Success - Post Login to GitHub Docker Registry
*DRYRUN* [goreleaser/goreleaser] ⭐ Run Post Login to Docker Registry
*DRYRUN* [goreleaser/goreleaser]   ✅  Success - Post Login to Docker Registry
*DRYRUN* [goreleaser/goreleaser] 🏁  Job succeeded