fix(traefik): add instance labels to GatewayClasses

The kubernetesGateway labelSelector applies to all watched resources
including GatewayClasses. Without traefik.io/instance labels, neither
Traefik instance could see or accept its own GatewayClass.

apps/base/traefik-system/gatewayclass-external.yaml

@@ -2,6 +2,8 @@
 apiVersion: gateway.networking.k8s.io/v1
 kind: GatewayClass
 metadata:
+  labels:
+    traefik.io/instance: external
   name: traefik-external
 spec:
   controllerName: traefik.io/gateway-controller

apps/base/traefik-system/gatewayclass-internal.yaml

@@ -2,6 +2,8 @@
 apiVersion: gateway.networking.k8s.io/v1
 kind: GatewayClass
 metadata:
+  labels:
+    traefik.io/instance: internal
   name: traefik-internal
 spec:
   controllerName: traefik.io/gateway-controller