Readiness probe (#1169)

Right now there are no readiness probes defined for connection pooler,
which means after a pod restart there is a short time window (between a
container start and connection pooler starting listening to a socket)
when a service can send queries to a new pod, but connection will be
refused. The pooler container is rather lightweight and it start to
listen immediately, so the time window is small, but still.

To fix this add a readiness probe for tcp socket opened by connection
pooler.

pkg/cluster/k8sres.go

@@ -2216,6 +2216,13 @@ func (c *Cluster) generateConnectionPoolerPodTemplate(spec *acidv1.PostgresSpec)
 			},
 		},
 		Env: envVars,
+		ReadinessProbe: &v1.Probe{
+			Handler: v1.Handler{
+				TCPSocket: &v1.TCPSocketAction{
+					Port: intstr.IntOrString{IntVal: pgPort},
+				},
+			},
+		},
 	}
 
 	podTemplate := &v1.PodTemplateSpec{