Publish Nexus Storage Service as a fat jar

[olivergrabinski]

• The Nexus Storage Service can be published locally as a fat jar by running sbt storage/Universal/publishLocal. The content of the archive contains the Nexus Storage Service as a far jar, the nexus-fixer, and the kanela agent. This should be all that is required to run the service (provided a JVM).
• The ci-snapshot pipeline is update to publish the snapshot version of the Storage Service. TBD whether we need this or not.
• The ci-release should publish the universal package (with the fat jar) upon a release; this needs to be confirmed when the next release is made.