Allow ExternalName services (#73)

This option allows the use of service type `ExternalName`:
https://kubernetes.io/docs/concepts/services-networking/service/#externalname

cluster/apps/networking/traefik/helm-release.yaml

@@ -54,6 +54,7 @@ spec:
     additionalArguments:
       - "--providers.kubernetesingress.ingressendpoint.ip=${SVC_TRAEFIK_ADDR}"
       - "--providers.kubernetescrd.allowexternalnameservices=true"
+      - "--providers.kubernetesingress.allowexternalnameservices=true"
     ports:
       traefik:
         expose: true