Create headless service associated with $SCOPE-config endpoint (#958)

if there is no service defined k8s assumes that endpoint is orphaned and removes it.
Patroni tries to create the service only in case if use_endpoints is enabled if the following cases:
1. Upon start
2. When it tries to (re-)create the config endpoint

If for some reason creation of the service has failed, Patroni will retry it on every cycle of HA loop. Usually it fails due to lack of permissions and if you don't want to give such permissions to the service account used by Patroni, you can create the service explicitly in the deployment manifest.

kubernetes/patroni_k8s.yaml

@@ -1,3 +1,15 @@
+# headless service to avoid deletion of patronidemo-config endpoint
+apiVersion: v1
+kind: Service
+metadata:
+  name: patronidemo-config
+  labels:
+    application: patroni
+    cluster-name: patronidemo
+spec:
+  clusterIP: None
+
+---
 apiVersion: apps/v1beta1
 kind: StatefulSet
 metadata:
@@ -173,6 +185,16 @@ rules:
   - patch
   - update
   - watch
+# The following privilege is only necessary for creation of headless service
+# for patronidemo-config endpoint, in order to prevent cleaning it up by the
+# k8s master. You can avoid giving this privilege by explicitly creating the
+# service like it is done in this manifest (lines 2..10)
+- apiGroups:
+  - ""
+  resources:
+  - services
+  verbs:
+  - create
 
 ---
 apiVersion: rbac.authorization.k8s.io/v1