examples: add example usage of prometheus-agent

Signed-off-by: paulfantom <pawel@krupa.net.pl>

examples/prometheus-agent.jsonnet

+local kp =
+  (import 'kube-prometheus/main.libsonnet') +
+  {
+    values+:: {
+      common+: {
+        namespace: 'monitoring',
+      },
+      prometheus+: {
+        version: '2.32.0',
+        resources: {
+          requests: { memory: '100Mi' },
+        },
+        enableFeatures: ['agent']
+      },
+    },
+    prometheus+: {
+      prometheus+: {
+        alerting:: {},
+        remoteWrite: {
+	  // Remote-write config
+        },
+      },
+    },
+  };
+
+{ 'setup/0namespace-namespace': kp.kubePrometheus.namespace } +
+{
+  ['setup/prometheus-operator-' + name]: kp.prometheusOperator[name]
+  for name in std.filter((function(name) name != 'serviceMonitor' && name != 'prometheusRule'), std.objectFields(kp.prometheusOperator))
+} +
+// serviceMonitor and prometheusRule are separated so that they can be created after the CRDs are ready
+{ 'prometheus-operator-serviceMonitor': kp.prometheusOperator.serviceMonitor } +
+{ 'prometheus-operator-prometheusRule': kp.prometheusOperator.prometheusRule } +
+{ 'kube-prometheus-prometheusRule': kp.kubePrometheus.prometheusRule } +
+{ ['blackbox-exporter-' + name]: kp.blackboxExporter[name] for name in std.objectFields(kp.blackboxExporter) } +
+{ ['grafana-' + name]: kp.grafana[name] for name in std.objectFields(kp.grafana) } +
+{ ['kube-state-metrics-' + name]: kp.kubeStateMetrics[name] for name in std.objectFields(kp.kubeStateMetrics) } +
+{ ['kubernetes-' + name]: kp.kubernetesControlPlane[name] for name in std.objectFields(kp.kubernetesControlPlane) }
+{ ['node-exporter-' + name]: kp.nodeExporter[name] for name in std.objectFields(kp.nodeExporter) } +
+{ ['prometheus-' + name]: kp.prometheus[name] for name in std.objectFields(kp.prometheus) } +
+{ ['prometheus-adapter-' + name]: kp.prometheusAdapter[name] for name in std.objectFields(kp.prometheusAdapter) }