logrotate: change postrotate script

Not clear how well the previous script worked.

The replacement was picked up from /etc/logrotate.d/rsyslog on Ubuntu
22.04 , which boils down to sending SIGHUP to rsyslog, which is the
classical way and is very likely to work. How broadly available is this
command remains to be seen.

debian/bluecherry.logrotate

@@ -7,6 +7,6 @@
 	delaycompress
 	compress
 	postrotate
-		reload rsyslog >/dev/null 2>&1 || true
+		/usr/lib/rsyslog/rsyslog-rotate
 	endscript
 }