Avoid syncing when possible (#1274)

Avoid extra syncing in case there are no changes in pooler requirements.
Add pooler specific labels to pooler secrets.
Add test case to check for pooler secret creation and deletion.

Co-authored-by: Rafia Sabih <rafia.sabih@zalando.de>

pkg/cluster/k8sres.go

@@ -1561,11 +1561,17 @@ func (c *Cluster) generateSingleUserSecret(namespace string, pgUser spec.PgUser)
 	}
 
 	username := pgUser.Name
+	lbls := c.labelsSet(true)
+
+	if username == constants.ConnectionPoolerUserName {
+		lbls = c.connectionPoolerLabels("", false).MatchLabels
+	}
+
 	secret := v1.Secret{
 		ObjectMeta: metav1.ObjectMeta{
 			Name:        c.credentialSecretName(username),
 			Namespace:   namespace,
-			Labels:      c.labelsSet(true),
+			Labels:      lbls,
 			Annotations: c.annotationsSet(nil),
 		},
 		Type: v1.SecretTypeOpaque,
@@ -1574,6 +1580,7 @@ func (c *Cluster) generateSingleUserSecret(namespace string, pgUser spec.PgUser)
 			"password": []byte(pgUser.Password),
 		},
 	}
+
 	return &secret
 }