Reduce log spam with LogLevelMax

[dhewg]

Quoting from systemd/systemd#19050:

The target use case for this feature is a service that runs on a timer
many times an hour, where the system administrator decides that writing
a generic success message to the journal every few minutes or seconds
adds no diagnostic value and isn't worth the clutter or disk I/O.

Looks like that PR is part of sytemd v249, but the option existed before.

I only got a 0,10,20,30,40,50 * * * * timer, but that's already enough to easily overlook more serious log entries.

[dhewg]

I gave it a try, works beautifully. How calm that journal now ;)