Add GitHub Workflow to build and push Docker image

[berney]

This PR adds a GitHub Workflow to build and push docker images to GHCR (GitHub's Container Registry).
It can be adapted to push to Docker Hub if you'd like.

The workflow extracts the labels from the git repo - from example if you create a git tag v1.0.0, the docker image will be tagged 1.0.0, as well as 1.0, and latest.
Pushes to the master branch will also trigger builds and will be labelled master and latest.

Event	Ref	Docker Tags
push	refs/heads/master	master, latest , sha-xxx
push tag	refs/tags/v1.2.3	1.2.3, 1.2, latest, sha-xxx

It builds a multi-arch image - there's an AMD64 and a ARM64 image.
Users will pull the one that matches their host architecture.

[adsanz]

Hey, since the project is on it's "baby steps" I didn't added any CICD yet, this is, to avoid creating dirty releases or to manage pre-releases.

I plan on release v1 in june, I'll come back to this PR then :)

Thanks again for your interest on the project!