Nakivo-prometheus-exporter

Quick release that adds the `SKIPPED` backup state for Prometheus, showing as warning in Grafana dashbard.

This release mainly adds an error message when API doesn't allow to be used because of licensing issues.

Also adds debugging and fixes a typo in the systemd unit file.

This release adresses an issue where object backup state is incertain if never run...
Thanks to vitorfulgencio for the catch.

So this is our first release of this exporter for Nakivo B&R.
Problably not enough tested (a couple of instances only), but here we are ^^