build + docker images

Hi 👋🏼 , would you be open to a PR replacing some of the `Makefile` with Goreleaser?

My reasoning is, it could "trim" the Makefile a bit and I would also be able to add multi-arch/platform Docker images easily? The reason why I'd like a Docker image is to be able to run `k0sctl` via Docker (or even k8s).

Start by reviewing the Makefile and the current k0sctl build and release process. Define which Makefile responsibilities Goreleaser should replace and how multi-architecture Docker images would be produced. Done means the proposed workflow supports running k0sctl through Docker or Kubernetes, with the scope agreed by maintainers.

Written by the indexing model from the issue text.