contrib/kube-prometheus: Create missing Prometheus operator alerts

jsonnet/kube-prometheus/alerts/alerts.libsonnet

 (import 'alertmanager.libsonnet') +
 (import 'general.libsonnet') +
 (import 'node.libsonnet') +
-(import 'prometheus.libsonnet')
+(import 'prometheus.libsonnet') +
+(import 'prometheus-operator.libsonnet')

jsonnet/kube-prometheus/alerts/prometheus-operator.libsonnet

+{
+  prometheusAlerts+:: {
+    groups+: [
+      {
+        name: 'prometheus-operator',
+        rules: [
+          {
+            alert: 'PrometheusOperatorAlertmanagerReconcileErrors',
+            expr: |||
+              rate(prometheus_operator_alertmanager_reconcile_errors_total{%(prometheusOperatorSelector)s}[5m]) > 0.01
+            ||| % $._config,
+            labels: {
+              severity: 'warning',
+            },
+            annotations: {
+              message: 'Errors while reconciling Alertmanager in {{$labels.namespace}} namespace.',
+            },
+            'for': '10m',
+          },
+          {
+            alert: 'PrometheusOperatorPrometheusReconcileErrors',
+            expr: |||
+              rate(prometheus_operator_prometheus_reconcile_errors_total{%(prometheusOperatorSelector)s}[5m]) > 0.01
+            ||| % $._config,
+            labels: {
+              severity: 'warning',
+            },
+            annotations: {
+              message: 'Errors while reconciling Prometheus in {{$labels.namespace}} namespace.',
+            },
+            'for': '10m',
+          },
+          {
+            alert: 'PrometheusOperatorNodeLookupErrors',
+            expr: |||
+              rate(prometheus_operator_node_address_lookup_errors_total{%(prometheusOperatorSelector)s}[5m]) > 0.01
+            ||| % $._config,
+            labels: {
+              severity: 'warning',
+            },
+            annotations: {
+              message: 'Errors while reconciling Prometheus in {{$labels.namespace}} namespace.',
+            },
+            'for': '10m',
+          },
+        ],
+      },
+    ],
+  },
+}