Automate release with Github Actions

[gaeljw]

Following a discussion initiated at #268 (comment), I suggest we setup an automated process for releases with Github Actions.

The natural candidate would be to use sbt-ci-release plugin that many other OSS project use. And trigger a release when a git tag is pushed.
This will require someone with the Sonatype credentials to enter them as secrets in the project.

I'll try to work on a draft of this in the coming days and I suggest we either "test it" live for the 3.0 release or if there's urgent demand for the 3.0 release, we'll create some 3.0.x releases with no code changes but only to test the Github workflow.