Allow systemd notifications from all member processes

By default the notifications are only allowed from the main process or any
child process that systemd finds. When the main process has not yet been
detected by systemd but MaxScale sends a notification, an error is logged
into the system journal. To prevent this, notifications from all member
processes should be allowed.

etc/maxscale.service.in

@@ -21,6 +21,7 @@ TimeoutStartSec=120
 LimitNOFILE=65535
 StartLimitBurst=0
 WatchdogSec=60s
+NotifyAccess=all
 
 # Only relevant when MaxScale is linked with -fsanitize=address
 Environment=ASAN_OPTIONS=abort_on_error=1