kube-prometheus: extract ServiceMonitors into single files

Starting with Kubernetes 1.6 `kubectl apply` works for TPRs so we can
start using it, therefore using multiple files is no issue.

manifests/prometheus/prometheus-k8s-service-monitor-kube-state-metrics.yaml

@@ -0,0 +1,19 @@
+apiVersion: monitoring.coreos.com/v1alpha1
+kind: ServiceMonitor
+metadata:
+  name: kube-state-metrics
+  namespace: monitoring
+  labels:
+    k8s-apps: http
+spec:
+  jobLabel: k8s-app
+  selector:
+    matchLabels:
+      k8s-app: kube-state-metrics
+  namespaceSelector:
+    matchNames:
+    - monitoring
+  endpoints:
+  - port: http-metrics
+    interval: 15s
+    honorLabels: true