Add instructions on testing metricbeat kubernetes module

metricbeat/module/kubernetes/_meta/test/docs/01_playground/ek_stack.yaml

@@ -0,0 +1,79 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  annotations:
+    deployment.kubernetes.io/revision: "1"
+  labels:
+    app: elasticsearch
+  name: elasticsearch
+  namespace: default
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: elasticsearch
+  strategy:
+    rollingUpdate:
+      maxSurge: 25%
+      maxUnavailable: 25%
+    type: RollingUpdate
+  template:
+    metadata:
+      labels:
+        app: elasticsearch
+    spec:
+      containers:
+        - image: docker.elastic.co/elasticsearch/elasticsearch:8.0.0-SNAPSHOT
+          imagePullPolicy: IfNotPresent
+          name: elasticsearch
+          env:
+            - name: "discovery.type"
+              value: "single-node"
+
+---
+apiVersion: v1
+kind: Service
+metadata:
+  labels:
+    app: elasticsearch
+  name: elasticsearch
+  namespace: default
+spec:
+  ports:
+    - port: 9200
+      protocol: TCP
+      targetPort: 9200
+  selector:
+    app: elasticsearch
+  sessionAffinity: None
+  type: ClusterIP
+
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  annotations:
+    deployment.kubernetes.io/revision: "1"
+  labels:
+    app: kibana
+  name: kibana
+  namespace: default
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: kibana
+  strategy:
+    rollingUpdate:
+      maxSurge: 25%
+      maxUnavailable: 25%
+    type: RollingUpdate
+  template:
+    metadata:
+      labels:
+        app: kibana
+    spec:
+      containers:
+        - image: docker.elastic.co/kibana/kibana:8.0.0-SNAPSHOT
+          imagePullPolicy: IfNotPresent
+          name: kibana