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-system/deployment.yaml

@@ -21,7 +21,7 @@ spec:
         runAsNonRoot: true
       containers:
         - name: operator
-          image: git.unkin.net/unkin/bind-operator:v0.1.2
+          image: git.unkin.net/unkin/bind-operator:v0.1.3
           args:
             - --metrics-bind-address=:8080
             - --health-probe-bind-address=:8081

apps/base/bind-system/kustomization.yaml

@@ -6,6 +6,6 @@ resources:
   - namespace.yaml
   # CRDs are pulled from the bind-operator repo at the matching tag rather than
   # vendored here, so they never drift from the operator.
-  - https://git.unkin.net/unkin/bind-operator/raw/tag/v0.1.1/config/crd/install.yaml
+  - https://git.unkin.net/unkin/bind-operator/raw/tag/v0.1.3/config/crd/install.yaml
   - rbac.yaml
   - deployment.yaml