Consolidate BIND DNS into one bind-internal namespace

Reshapes the three DNS tiers from separate ns-* namespaces into a single
bind-internal namespace and renames the StatefulSets, and scopes the TSIG
keys to their cluster (needs the clusterRef field from operator v0.1.3).

- move the 3 clusters + zones + keys into apps/base/bind-internal:
  BindCluster names bind-authoritative / bind-resolvers / bind-externaldns
  (= StatefulSet names), LBs kept on .6/.7/.8, external-dns hostnames renamed
- add clusterRef to the transfer-key (bind-authoritative) and externaldns-key
  (bind-externaldns) TSIG keys so they no longer leak across clusters
- remove the old ns-auth / ns-resolver / ns-externaldns apps
- ApplicationSet + AppProject: replace the three ns-* entries with bind-internal
- bump bind-system operator to v0.1.3 (CRD install link + image) so the CRDs
  understand the new clusterRef field
- operator stays in bind-system (unchanged)

apps/base/bind-internal/resolvers/cluster.yaml

@@ -0,0 +1,29 @@
+---
+# Recursive resolvers (replaces the 3x Puppet only-resolver servers).
+# Three identical recursive servers; no zone replication.
+apiVersion: bind.unkin.net/v1alpha1
+kind: BindCluster
+metadata:
+  name: bind-resolvers
+  namespace: bind-internal
+spec:
+  mode: resolver
+  replicas: 3
+  storageClassName: cephrbd-fast-delete
+  storageSize: 1Gi
+  service:
+    type: LoadBalancer
+    annotations:
+      purelb.io/service-group: common
+      purelb.io/addresses: 198.18.200.7
+      external-dns.alpha.kubernetes.io/hostname: bind-resolvers.k8s.syd1.au.unkin.net
+  forwarders:
+    - 1.1.1.1
+    - 9.9.9.9
+  resources:
+    requests:
+      cpu: 100m
+      memory: 128Mi
+    limits:
+      cpu: "1"
+      memory: 512Mi

apps/base/bind-internal/resolvers/kustomization.yaml

@@ -0,0 +1,6 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - cluster.yaml