Deploying Maven artifacts

We're getting a lot of questions about artifacts, particularly from the Java community using Maven. We don't need to replace artifactory to make this work. Let's make a blog post (and documentation) for deploying Maven artifacts using GitLab CI.

Here's even a post from Travis on the subject which is probably exactly how you'd do it with GitLab CI:

https://blog.travis-ci.com/2017-03-30-deploy-maven-travis-ci-packagecloud/

/cc @bikebilly