Add kube-router annotations (#3533)

docs/kube-router.md

...ory/sample/group_vars/k8s-cluster/k8s-net-kube-router.yml

roles/network_plugin/kube-router/defaults/main.yml

roles/network_plugin/kube-router/tasks/annotate.yml

roles/network_plugin/kube-router/tasks/main.yml