Add a primary (write) Service routing to pod-0

Secondaries reject RFC2136/nsupdate writes, but the read Service round-
robins across all pods. Add an optional per-cluster write endpoint that
targets only the primary pod (ordinal 0) via the StatefulSet pod-name
label. Reads keep using the all-pods Service.

- api: BindCluster.spec.primaryService (*ClusterServiceSpec) — ClusterIP
  for in-cluster writers (external-dns) or LoadBalancer for external
- reconcilePrimaryService creates <cluster>-primary selecting pod-0 when
  set, deletes it when unset
- regenerate CRDs + install.yaml

api/v1alpha1/zz_generated.deepcopy.go

@@ -301,6 +301,11 @@ func (in *BindClusterSpec) DeepCopyInto(out *BindClusterSpec) {
 	}
 	in.Resources.DeepCopyInto(&out.Resources)
 	in.Service.DeepCopyInto(&out.Service)
+	if in.PrimaryService != nil {
+		in, out := &in.PrimaryService, &out.PrimaryService
+		*out = new(ClusterServiceSpec)
+		(*in).DeepCopyInto(*out)
+	}
 	if in.NodeSelector != nil {
 		in, out := &in.NodeSelector, &out.NodeSelector
 		*out = make(map[string]string, len(*in))