Add workflow to build and push image to GCP Artifact Registry

.github/workflows/build-and-push.yml

@@ -0,0 +1,46 @@
+name: Build and push image to GCP
+
+on: push #TODO change to on: push main after testing
+
+jobs:
+  docker_build_push_gcp:
+    name: 'Docker build and push to GCP'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: 'read'
+      id-token: 'write'
+    steps:
+      - uses: 'actions/checkout@v4'
+
+      - name: Authenticate to Google Cloud
+        id: auth
+        uses: 'google-github-actions/auth@v2'
+        with:
+          credentials_json: ${{ secrets.GCS_ACC_KEY_JSON }}
+
+      # To optionally display info about current gcloud environment
+      - name: 'Set up Cloud SDK'
+        uses: "google-github-actions/setup-gcloud@v1"
+
+      - name: "Use gcloud CLI"
+        run: "gcloud info"
+
+      # Auth Docker to access the artifact registry
+      - name: "Docker auth"
+        run: |-
+          gcloud auth configure-docker europe-north1-docker.pkg.dev --quiet
+
+      - name: Login to GAR
+        uses: docker/login-action@v3
+        with:
+          registry: europe-north1-docker.pkg.dev
+          username: _json_key
+          password: ${{ secrets.GCS_ACC_KEY_JSON }}
+
+      - name: Push to Google Artifact Registry
+        uses: docker/build-push-action@v2
+        with:
+          push: true
+          tags: |
+            europe-north1-docker.pkg.dev/spire-ros-5lmr/kv-ros/backstage:latest
+