WIP NEXUS-5961: plexusplugin plugin

WIP

A simple plugin using Plexus components that proves that Plexus and DI still works with them. IT to boot it up and test drive.


Issue:
https://issues.sonatype.org/browse/NEXUS-5961

CI:
https://bamboo.zion.sonatype.com/browse/NX-OSSF78