Pin binddns-auth service to a dedicated IP

DNS (UDP/53) can't route via a shared gateway yet (no UDPRoute), so the
service needs its own LoadBalancer address instead of a pool-assigned one.

- pin purelb.io/addresses 198.18.200.6 (common pool)

apps/base/binddns-auth/cluster.yaml

@@ -15,6 +15,7 @@ spec:
     type: LoadBalancer
     annotations:
       purelb.io/service-group: common
+      purelb.io/addresses: 198.18.200.6
       external-dns.alpha.kubernetes.io/hostname: ns-auth.k8s.syd1.au.unkin.net
   resources:
     requests: