Examples: Add v1 Kubernetes bluegreen example

examples/v1/kubernetes/bluegreen/app.pipecd.yaml

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+apiVersion: pipecd.dev/v1beta1
+kind: Application
+spec:
+  name: bluegreen
+  labels:
+    env: example
+    team: product
+  pipeline:
+    stages:
+      # Roll out CANARY variant with the same number of replicas as PRIMARY.
+      - name: K8S_CANARY_ROLLOUT
+        with:
+          replicas: 100%
+      # Route all traffic to CANARY variant.
+      - name: K8S_TRAFFIC_ROUTING
+        with:
+          canary: 100
+      # Wait for a manual approval on the web console before promoting.
+      - name: WAIT_APPROVAL
+        with:
+          minApproverNum: 1
+          # Replace with real usernames.
+          approvers:
+            - example-user
+      # Roll out PRIMARY variant to the new version.
+      - name: K8S_PRIMARY_ROLLOUT
+      # Route all traffic back to PRIMARY variant.
+      - name: K8S_TRAFFIC_ROUTING
+        with:
+          primary: 100
+      # Clean up CANARY variant workloads.
+      - name: K8S_CANARY_CLEAN
+  plugins:
+    kubernetes:
+      input:
+        manifests:
+          - deployment.yaml
+          - service.yaml
+  description: |
+    This app demonstrates how to deploy a Kubernetes app by BlueGreen strategy without requiring any mesh.
+    References: [adding a new app](https://pipecd.dev/docs-v1.0.x/user-guide/managing-application/adding-an-application/), [app configuration](https://pipecd.dev/docs-v1.0.x/user-guide/managing-application/configuration-reference/)

examples/v1/kubernetes/bluegreen/deployment.yaml

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+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: bluegreen
+  labels:
+    app: bluegreen
+spec:
+  replicas: 2
+  selector:
+    matchLabels:
+      app: bluegreen
+      pipecd.dev/variant: primary
+  template:
+    metadata:
+      labels:
+        app: bluegreen
+        pipecd.dev/variant: primary
+    spec:
+      containers:
+      - name: helloworld
+        image: ghcr.io/pipe-cd/helloworld:v0.32.0
+        args:
+          - server
+        ports:
+        - containerPort: 9085

examples/v1/kubernetes/bluegreen/service.yaml

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+apiVersion: v1
+kind: Service
+metadata:
+  name: bluegreen
+spec:
+  selector:
+    app: bluegreen
+    pipecd.dev/variant: primary
+  ports:
+    - protocol: TCP
+      port: 9085
+      targetPort: 9085