Harmonise postrotate script in logrotate config with stock el packages

[qha]

On el8 and el9 the postrotate script in logrotate config seem to be pretty much equivalent to that shipped with the stock (rh)el packages. They are not identical however which will keep sharedscripts from merging them with other postrotate scripts that try to harmonise with the stock packages.

(We try to do this for a /var/log/debug that we added to our rsyslog config.)

The differences are:
systemctl kill -s HUP rsyslog.service in the Adiscon packages vs:
/usr/bin/systemctl kill -s HUP rsyslog.service >/dev/null 2>&1 || true in the stock packages.

[qha]

(On el7 i presume #42 makes this a nonstarter.)

[rgerhards]

@alorbach sounds good to me, what do you think?

[alorbach]

We can adapt the changes from the stock packages, they look reasonable to me.