Suggestion: Create runnable jar by default

[fwilhe2]

I like this archetype :+1:

I guess this might be a bit controversial, not sure if this is inside the scope of this archetype, but I'd propose to add a main method and set it so we get a jar that can be run with java -jar target/app.jar.

Honestly that is something where I always need to look up how to do it again, so it would be really nice if it was an (optional?) feature of this archetype.