Docker: arm64 images

[robvanoostenrijk]

I would have normally raised a PR for this, but the go-release workflow is pulled in from another repo and might be used in other places as well.

It would be nice to have the docker image not only build for amd64, but also arm64.

An approach on how to achieve this with a .goreleaser.yaml file can be found here:
https://pet2cattle.com/2023/08/golang-releaser

[itzg]

I'll queue that up. Thanks but I already have multi-architecture image builds in other repos

https://github.com/itzg/mc-router/blob/master/.goreleaser.yml

The shared workflow imposes no constraint on that.