test: Add apiserver-ilb-zones flavor for zone-redundant LB E2E test

Create a new cluster template flavor that extends apiserver-ilb
and adds availabilityZones configuration to all load balancers
(APIServerLB, NodeOutboundLB, ControlPlaneOutboundLB).

This fixes the optional E2E test for zone-redundant load balancers
by using a dedicated template with zones pre-configured instead of
relying on an unused environment variable.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: bryan-cox

templates/cluster-template-apiserver-ilb-zones.yaml

@@ -0,0 +1,11 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+namespace: default
+resources:
+- ../apiserver-ilb
+
+patches:
+- path: patches/lb-zones.yaml
+
+sortOptions:
+  order: fifo

templates/flavors/apiserver-ilb-zones/kustomization.yaml

@@ -0,0 +1,21 @@
+apiVersion: infrastructure.cluster.x-k8s.io/v1beta1
+kind: AzureCluster
+metadata:
+  name: ${CLUSTER_NAME}
+spec:
+  networkSpec:
+    apiServerLB:
+      availabilityZones:
+        - "1"
+        - "2"
+        - "3"
+    nodeOutboundLB:
+      availabilityZones:
+        - "1"
+        - "2"
+        - "3"
+    controlPlaneOutboundLB:
+      availabilityZones:
+        - "1"
+        - "2"
+        - "3"