chore(CI/CD): Add pr-image-builder workflow

.github/workflows/pr-image-builder.yaml

@@ -0,0 +1,54 @@
+name: Build and Push Docker Image
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+jobs:
+  # run_unit_tests:
+  #   name: Run unit tests
+  #   uses: l7mp/stunner-gateway-operator/.github/workflows/test.yml@main
+
+  push_to_registry:
+    name: Push Docker image to DockerHub
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@v2
+        with:
+          username: ${{ secrets.DOCKER_USER }}
+          password: ${{ secrets.DOCKER_TOKEN }}
+
+      - name: Build and Push Docker Image
+        id: docker_build
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: |
+            l7mp/stunner-gateway-operator:pr-${{ github.event.pull_request.number }}
+
+      - name: Comment on PR
+        if: success() && github.event_name == 'pull_request'
+        uses: actions/github-script@v6
+        with:
+          script: |
+            const prNumber = context.issue.number;
+            const comment = `The Docker image for this pull request (#${prNumber}) has been successfully built and pushed to DockerHub as \`l7mp/stunner-gateway-operator:pr-${prNumber}\`.`;
+            github.rest.issues.createComment({
+              issue_number: prNumber,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: comment,
+            });