Use a new systemd timer on CentOS 8 and above

The files

/etc/logrotate.d/lpadmincern
/etc/cron.daily/lpadmincern

are replaced with units

lpadmincern.service
lpadmincern.timer

Some of options in /etc/sysconfig/lpadmincern are redundant now and comments have been added to that affect.

One change in behaviour.

 /usr/sbin/lpadmincern -u 

used to run on installation and every upgrade. It now only runs on installation in the background if the node has or once the node has been up for 10 minutes. It does not run on upgrade of the package. This is a good thing.

• Avoiding hanging the rpm installations for around 20 minutes while this things run is good.
• There's a timer to update with new version of the software anyway.

Changes apply to eight and newer only