Feature request: Automated Builds + Publishing of docker image and release tarball via Github Actions

[t-lo]

This is a good issue to start with if you'd like to become a contributor to the mailserver project.

Goal of this feature request is to automate build and publishing of new Mailserver releases. There's a script that does most of this work already - the logic of that script would need to be converted into a Github Action.

[4censord]

Do you only want releases to be build, or also e.g. pullrequests?

[t-lo]

I think per tag is fine for now. Since only the docker image is built and no real tests are run, build results might not add that much value to a PR.