Publish artifacts to github maven repo with github actions

[shaneikennedy]

Publishing artifacts makes it easy for plugin systems to be configured to auto-install this language server when groovy files are detected

Two things in this PR:

1. an editor config so that I don't screw up the formatting
2. gradle config + github action to publish artifacts on the github maven repository, following the guide here

If you decide to accept this PR, in order for it to work you'll need to add the environment variable GITHUB_TOKEN to your github actions (GITHUB_ACTOR is also required in this PR but it's a default argument for every github actions build)

The GITHUB_TOKEN secret is set to an access token for the repository each time a job in a workflow begins. You should set the permissions for this access token in the workflow file to grant read access for the contents scope and write access for the packages scope. For more information, see "Automatic token authentication."