include upload of xar artifact to fusiondb.com in build process

[duncdrum]

mvn release should upload the xar to the downloads section on fusiondb.com which means anybody doing releases needs valid credentials.

While we're at it I still think doing the same to the releases section here on Github is a good idea, i.e. attach the xar as a release artifact.

This is still doing it manually, but the same command could/should be run from CI in the future.