Improve kubernetes external name service support

Co-authored-by: jbdoumenjou <jb.doumenjou@gmail.com>

pkg/provider/kubernetes/crd/fixtures/with_externalname_with_https.yml

@@ -0,0 +1,16 @@
+apiVersion: traefik.containo.us/v1alpha1
+kind: IngressRoute
+metadata:
+  name: test.route
+  namespace: default
+
+spec:
+  entryPoints:
+    - foo
+
+  routes:
+  - match: Host(`foo.com`)
+    kind: Rule
+    services:
+    - name: external-svc-with-https
+      port: 443