Add a CI job to test that running Electric using a Docker image works (#2762)

We've had a couple of commits in the past where Electric was working
fine in dev but ended up failing on startup when run as a Docker
container. This CI job is designed to verify that Electric starts up and
reaches healthy state when running inside a container.

Author: alco

.github/workflows/docker_image_smoketest.yml

@@ -0,0 +1,60 @@
+name: Electric Docker Image Smoke Test
+
+on:
+  pull_request:
+    paths-ignore:
+      - "**/README.md"
+
+jobs:
+  docker_image_smoketest:
+    name: Docker image smoke test
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: "postgres:17-alpine"
+        env:
+          POSTGRES_PASSWORD: password
+        ports:
+          - 5432:5432
+
+    steps:
+      - name: "Set PG settings"
+        run: |
+          docker exec ${{ job.services.postgres.id }} sh -c 'echo "wal_level=logical" >> /var/lib/postgresql/data/postgresql.conf'
+          docker restart ${{ job.services.postgres.id }}
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: actions/checkout@v4
+
+      - uses: docker/build-push-action@v6
+        with:
+          context: packages/sync-service
+          push: false
+          load: true
+          tags: "electric-test-image"
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+      - name: "Run the built image"
+        run: |
+          docker run \
+            --rm \
+            --net host \
+            --name electric \
+            -e ELECTRIC_USAGE_REPORTING=false \
+            -e ELECTRIC_INSECURE=true \
+            -e DATABASE_URL='postgresql://postgres:password@localhost:5432?sslmode=disable' \
+            -d \
+            electric-test-image
+
+      - name: Wait for the container to reach healthy status
+        uses: stringbean/docker-healthcheck-action@v3
+        with:
+          container: electric
+          require-status: running
+          require-healthy: true
+          wait-time: 20
+
+      - name: Dump container logs
+        run: docker logs electric