fix(traefik): replace invalid controllername flag with labelSelector for v3 (#125)

Remove --providers.kubernetesgateway.controllername which does not exist in
Traefik v3, update GatewayClass controllerName to the standard v3 value, and
use labelSelector on each instance's kubernetesGateway provider to differentiate
internal vs external traffic.

Reviewed-on: #125

apps/overlays/au-syd1/traefik-system/values-external.yaml

@@ -1,8 +1,6 @@
 image:
   tag: v3.7.0
 
-additionalArguments:
-  - "--providers.kubernetesgateway.controllername=traefik.io/gateway-controller-external"
 
 podDisruptionBudget:
   enabled: true
@@ -29,6 +27,7 @@ providers:
     experimentalChannel: false
     namespaces: []
     nativeLBByDefault: false
+    labelSelector: "traefik.io/instance=external"
 
 logs:
   access:

apps/overlays/au-syd1/traefik-system/values-internal.yaml

@@ -1,8 +1,6 @@
 image:
   tag: v3.7.0
 
-additionalArguments:
-  - "--providers.kubernetesgateway.controllername=traefik.io/gateway-controller-internal"
 
 podDisruptionBudget:
   enabled: true
@@ -29,6 +27,7 @@ providers:
     experimentalChannel: false
     namespaces: []
     nativeLBByDefault: false
+    labelSelector: "traefik.io/instance=internal"
 
 logs:
   access: