kube-prometheus: fix correct selector

manifests/prometheus/prometheus-k8s-service-monitor-alertmanager.yaml

@@ -3,7 +3,7 @@ kind: ServiceMonitor
 metadata:
   name: alertmanager
   labels:
-    app: alertmanager
+    k8s-app: alertmanager
 spec:
   selector:
     matchLabels:

manifests/prometheus/prometheus-k8s-service-monitor-prometheus.yaml

@@ -3,7 +3,7 @@ kind: ServiceMonitor
 metadata:
   name: prometheus
   labels:
-    app: prometheus
+    k8s-app: prometheus
 spec:
   selector:
     matchLabels:

manifests/prometheus/prometheus-k8s.yaml

@@ -9,7 +9,7 @@ spec:
   version: v1.7.0
   serviceAccountName: prometheus-k8s
   serviceMonitorSelector:
-    matchExpression:
+    matchExpressions:
     - {key: k8s-app, operator: Exists}
   ruleSelector:
     matchLabels: