Add "app" and "run" labels to prometheus targets

This makes it possible to filter metrics per service, for example

up{run=~"zuul.*"}

Change-Id: I37f0b915635276badd3fcaee48d63946678e29dd

controllers/libs/monitoring/monitoring.go

@@ -351,6 +351,7 @@ func MkPodMonitor(name string, ns string, ports []string, selector metav1.LabelS
 		Spec: monitoringv1.PodMonitorSpec{
 			Selector:            selector,
 			PodMetricsEndpoints: endpoints,
+			PodTargetLabels:     []string{"app", "run"},
 		},
 	}
 }