Docs: kube prometheus jsonnet (#198)

Signed-off-by: Christian Beneke <christian.beneke@traderepublic.com>
Signed-off-by: Cody Belcher <cody.t.belcher@gmail.com>

jsonnet/custom-prometheus.jsonnet

@@ -0,0 +1,40 @@
+{
+  // Add Lens metric relabelings for custom prometheus instances installed with kube-prometheus
+  // https://github.com/lensapp/lens/blob/master/troubleshooting/custom-prometheus.md
+  nodeExporter+:: {
+    serviceMonitor+: {
+      spec+: {
+        endpoints: std.map(function(endpoint)
+          if endpoint.port == "https" then
+            endpoint {
+              relabelings+: [
+                {
+                  action: 'replace',
+                  regex: '(.*)',
+                  replacement: '$1',
+                  sourceLabels: ['__meta_kubernetes_pod_node_name'],
+                  targetLabel: 'kubernetes_node',
+                }
+              ],
+            }
+          else
+            endpoint,
+          super.endpoints
+        ),
+      },
+    },
+  },
+  prometheus+:: {
+    serviceMonitorKubelet+: {
+      spec+: {
+        metricRelabelings+: [
+          {
+            action: 'replace',
+            sourceLabels: ['node'],
+            targetLabel: 'instance',
+          },
+        ],
+      },
+    },
+  },
+}