Add CI/CD workflows & publish Docker image for latest head

[dnsmichi]

Hi,

I'd suggest to add a workflow based on existing actions in https://github.com/actions-rs/cargo to automatically build PRs, and the default branch.

The second step is to build the Dockerfile and publish it: https://docs.github.com/en/actions/publishing-packages/publishing-docker-images#publishing-images-to-docker-hub

On the default branch, tag the image as nightly or latest. Then users can use the Docker image alias in https://github.com/ogham/dog#container-image That way, no releases need to be tagged and those who want to run latest, can do so.

The actions workflow could also be extended to tagging nightly builds, but not sure how to get there with GitHub actions.