check_dns: better time measurement

alpine does not output ms using date, therefore we use perl to get a more
accurate measurement of the dns response time.
The script output is now even more similar to nagios check_dns.

docker-compose.yml

@@ -521,7 +521,7 @@ services:
         - /lib/modules:/lib/modules:ro
 
     watchdog-mailcow:
-      image: ghcr.io/mailcow/watchdog:2.09
+      image: ghcr.io/mailcow/watchdog:2.10
       dns:
         - ${IPV4_NETWORK:-172.22.1}.254
       tmpfs: