Add quickstart sample for private AKS cluster with custom DNS

quickstart/301-aks-private-cluster/dns-zone.tf

@@ -0,0 +1,13 @@
+resource "null_resource" "dns_zone_link" {
+
+  provisioner "local-exec" {
+    interpreter = ["bash"]
+    command = "dns-zone-link.sh"
+
+    environment = {
+      DNS_VNET = "${var.custom_dns_vnet_id}"
+      AKS_RESOURCE_GROUP="${var.resource_group_name}"
+      AKS_CLUSTER_NAME="${var.cluster_name}"
+    }
+  }
+}