Logging to systemd-journald misses detail fields

[oxzi]

When running icinga-notifications supervised by systemd or explicitly setting logging.output: systemd-journald, the logging fields containing the details are missing.

This was first attacked in #254, but should now be solved via Icinga/icinga-go-library#48. Afterwards, the icinga-go-library must be bumped.

To mitigate this issue in the meantime, logging.output: console can be configured.