feat(vault): switch to Kubernetes service registration (#171)

Replaces Consul service registration with the native Kubernetes provider so Vault labels its own pods with active/standby/perf-standby status without requiring a Consul dependency.

## Changes
- `values.yaml`: swap `service_registration "consul"` for `service_registration "kubernetes" {}`, add `VAULT_K8S_NAMESPACE` and `VAULT_K8S_POD_NAME` env vars via downward API
- `role_k8s-service-registration.yaml`: Role + RoleBinding granting the `vault` service account `get`/`update`/`patch` on pods
- `kustomization.yaml`: include new RBAC file

Reviewed-on: #171

apps/overlays/au-syd1/vault/values.yaml

@@ -40,9 +40,7 @@ server:
           }
         }
 
-        service_registration "consul" {
-          address = "consul-server.consul.svc.cluster.local:8500"
-        }
+        service_registration "kubernetes" {}
 
   dataStorage:
     enabled: true
@@ -50,6 +48,14 @@ server:
     storageClass: cephrbd-fast-delete
     accessMode: ReadWriteOnce
 
+  extraEnv:
+    - name: VAULT_K8S_NAMESPACE
+      value: vault
+    - name: VAULT_K8S_POD_NAME
+      valueFrom:
+        fieldRef:
+          fieldPath: metadata.name
+
   statefulSet:
     securityContext:
       container: