Add prometheus endpoints for k3s components

admin/prometheus_kubernetes_values.yaml

+# K3s doesn't provide these services as normal kubernetes services
+# See: https://github.com/rancher/k3s/issues/425#issuecomment-672019664
+kubeControllerManager:
+  endpoints:
+  - "128.104.110.154"
+
+kubeEtcd:
+  endpoints:
+  - "128.104.110.154"
+
+kubeScheduler:
+  endpoints:
+  - "128.104.110.154"
+
+kubeProxy:
+  endpoints:
+  - "128.104.110.154"
+
 alertmanager:
   ## Alertmanager configuration directives
   ## ref: https://prometheus.io/docs/alerting/configuration/#configuration-file