feature(docker): Create docker container and push to ghcr

[heliocastro]

@goneall Please consider make the gh packages repository for spdx public, so anyone can pull this image without the need to signin on github

[goneall]

@heliocastro I like the idea of creating a docker image. I personally don't have any experience with the GitHub action for publishing the docker image - so I have a couple questions:

• What environment variables and secrets need to be setup in GitHub?
• Should we only push released versions (which are always tagged) or push all versions?

[heliocastro]

@heliocastro I like the idea of creating a docker image. I personally don't have any experience with the GitHub action for publishing the docker image - so I have a couple questions:

• What environment variables and secrets need to be setup in GitHub?

No need, for this github already provide the necessary secrets for the repo. Is already on the PR. Look:

      - name: Login to GitHub Container Registry
        uses: docker/login-action@v2
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

Where's actor is spdx ( owner of the repo ) and password is generated by gh actions.

• Should we only push released versions (which are always tagged) or push all versions?
  In the PR, since you do not have a release branch, i went to all push's to the master.
  Tagging is automated one coming from this action: https://github.com/docker/metadata-action, so i'm preparing the next version to be built only when you tag the release.

[heliocastro]

@goneall Done, the current PR will build only when you add a tag v, and you don't need to care to modify the version on docker file.

[goneall]

Thanks @heliocastro - I'll go ahead and merge.

I'll may do a release relatively soon.