Deploy bind-operator and three BIND DNS tiers

Adds the bind-operator and the three BindClusters that replace the
Puppet-managed BIND estate (authoritative / resolver / external-dns).

- add apps/base/bind-system: 9 CRDs, operator Deployment, RBAC (ns bind-system)
- add apps/base/binddns-auth: authoritative BindCluster + catalog zone + TSIG key
- add apps/base/binddns-resolver: recursive-resolver BindCluster with forwarders
- add apps/base/binddns-externaldns: dynamic (RFC2136) BindCluster + TSIG key
- add au-syd1 overlays for all four apps
- register the four apps in the platform ApplicationSet
- add binddns-* namespaces to the platform AppProject destinations
- add schemas/bind.unkin.net/*.json so kubeconform validates the new CRs

DNS Services are LoadBalancer via PureLB. TSIG key material is generated by
the operator into Secrets at runtime (no plain Secrets in git).

apps/base/binddns-externaldns/cluster.yaml

@@ -0,0 +1,25 @@
+---
+# external-dns tier (replaces the 3x Puppet external-dns servers). The primary
+# accepts RFC2136 TSIG updates from external-dns; secondaries replicate.
+apiVersion: bind.unkin.net/v1alpha1
+kind: BindCluster
+metadata:
+  name: externaldns
+  namespace: binddns-externaldns
+spec:
+  mode: dynamic
+  replicas: 3
+  storageClassName: cephrbd-fast-delete
+  storageSize: 1Gi
+  service:
+    type: LoadBalancer
+    annotations:
+      purelb.io/service-group: dmz
+      external-dns.alpha.kubernetes.io/hostname: ns-ext.k8s.syd1.au.unkin.net
+  resources:
+    requests:
+      cpu: 100m
+      memory: 128Mi
+    limits:
+      cpu: "1"
+      memory: 512Mi

apps/base/binddns-externaldns/kustomization.yaml

@@ -0,0 +1,8 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - namespace.yaml
+  - tsigkey.yaml
+  - cluster.yaml

apps/base/binddns-externaldns/namespace.yaml

@@ -0,0 +1,5 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: binddns-externaldns

apps/base/binddns-externaldns/tsigkey.yaml

@@ -0,0 +1,10 @@
+---
+# Key that external-dns (and DNSRecord objects) use to send RFC2136 dynamic
+# updates to the primary. The operator generates the material into a Secret.
+apiVersion: bind.unkin.net/v1alpha1
+kind: BindTSIGKey
+metadata:
+  name: externaldns-key
+  namespace: binddns-externaldns
+spec:
+  algorithm: hmac-sha256