Add Cloud Build configuration for dispatcher pattern

.cloudbuild/build.yaml

@@ -0,0 +1,34 @@
+steps:
+  - name: 'gcr.io/cloud-builders/docker'
+    args: ['buildx', 'create', '--driver', 'docker-container', '--name', 'multiarch', '--use']
+
+  - name: 'gcr.io/cloud-builders/docker'
+    entrypoint: 'bash'
+    args:
+      - '-c'
+      - |
+        docker buildx build --platform linux/amd64,linux/arm64 \
+          -t ${_AR_REGION}-docker.pkg.dev/$PROJECT_ID/${_AR_REPO_NAME}/${_IMAGE_NAME}:latest \
+          -f Dockerfile \
+          --push ctx
+
+  - name: 'gcr.io/cloud-builders/docker'
+    entrypoint: 'bash'
+    secretEnv: ['GH_PAT']
+    args:
+      - '-c'
+      - |
+        echo $$GH_PAT | docker login ghcr.io -u $_REGISTRY_USER --password-stdin && \
+        docker buildx imagetools create \
+          -t ghcr.io/$_REGISTRY_USER/$_IMAGE_NAME:latest \
+          ${_AR_REGION}-docker.pkg.dev/$PROJECT_ID/${_AR_REPO_NAME}/${_IMAGE_NAME}:latest && \
+        docker logout ghcr.io
+
+availableSecrets:
+  secretManager:
+    - versionName: projects/$PROJECT_ID/secrets/alpine-cli-ghcr-token/versions/latest
+      env: 'GH_PAT'
+
+options:
+  logging: CLOUD_LOGGING_ONLY
+  substitutionOption: 'ALLOW_LOOSE'