Test the Jouranld input in a variety of Linux distros

The Journald input requires calls `journalctl` binary from the host, we use a number of features from `jouranlctl`, some of them might not be available on all Linux distributions officially supported by Filebeat. Having automated integration tests on at least the oldest version of each Linux distribution supported can help us to prevent bugs like https://github.com/elastic/beats/issues/48152.

The tests don't need to run all the time, only when there are changes to the journald input (`filebeat/inputs/journald`)