Add primary (write) Services to authoritative + externaldns (#229)

**Stacked on #228** (needs operator v0.1.5). Merge #228 first; the diff collapses to just this after.

## Why
Writes (RFC2136/nsupdate) must go to pod-0 — the round-robin read Service would land them on a secondary (rejected). Adds a dedicated write endpoint per cluster (operator v0.1.5 `primaryService`).

## Changes
- `bind-authoritative`: LoadBalancer write endpoint on **198.18.200.9** (`bind-authoritative-primary`)
- `bind-externaldns`: ClusterIP write endpoint (`bind-externaldns-primary`, for in-cluster writers)
- regenerate the bindcluster kubeconform schema (primaryService + externalTrafficPolicy)

## Deferred
external-dns is **not** repointed at `bind-externaldns-primary` yet: it authenticates with the existing TSIG key, which the operator-generated key won't match until the planned Vault-sync + secret-reflection features exist. Until then external-dns keeps writing to the puppet externaldns.

## Validated
kustomize build + kubeconform (3 BindClusters valid against the v0.1.5 schema).

---------

Co-authored-by: BenVincent <benvin@main.unkin.net>
Reviewed-on: #229
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

schemas/bind.unkin.net/bindcluster_v1alpha1.json

@@ -692,6 +692,35 @@
           },
           "type": "object"
         },
+        "primaryService": {
+          "properties": {
+            "annotations": {
+              "additionalProperties": {
+                "type": "string"
+              },
+              "type": "object"
+            },
+            "externalTrafficPolicy": {
+              "enum": [
+                "Cluster",
+                "Local"
+              ],
+              "type": "string"
+            },
+            "loadBalancerIP": {
+              "type": "string"
+            },
+            "type": {
+              "enum": [
+                "ClusterIP",
+                "LoadBalancer",
+                "NodePort"
+              ],
+              "type": "string"
+            }
+          },
+          "type": "object"
+        },
         "recursion": {
           "type": "boolean"
         },
@@ -765,6 +794,13 @@
               },
               "type": "object"
             },
+            "externalTrafficPolicy": {
+              "enum": [
+                "Cluster",
+                "Local"
+              ],
+              "type": "string"
+            },
             "loadBalancerIP": {
               "type": "string"
             },