Add a logfile entry to the NSD conf file (#1434)

Having a log file can help debugging when something goes wrong and
NSD doesn't fail or MiaB doesn't notify you.

See
https://discourse.mailinabox.email/t/dns-email-domain-becomes-inaccessible-every-few-hours/3770

setup/dns.sh

@@ -26,6 +26,7 @@ cat > /etc/nsd/nsd.conf << EOF;
 # Do not edit. Overwritten by Mail-in-a-Box setup.
 server:
   hide-version: yes
+  logfile: "/var/log/nsd.log"
 
   # identify the server (CH TXT ID.SERVER entry).
   identity: ""
@@ -41,6 +42,18 @@ server:
 
 EOF
 
+# Add log rotation
+cat > /etc/logrotate.d/nsd <<EOF;
+/var/log/nsd.log {
+  weekly
+  missingok
+  rotate 12
+  compress
+  delaycompress
+  notifempty
+}
+EOF
+
 # Since we have bind9 listening on localhost for locally-generated
 # DNS queries that require a recursive nameserver, and the system
 # might have other network interfaces for e.g. tunnelling, we have