Add CI workflow to build and push Docker images

On every release, a new image, containing the latest PyPI package, is
built and pushed to Docker Hub:
https://hub.docker.com/r/upstreamdata/goosebit

.github/workflows/docker.yml

@@ -0,0 +1,58 @@
+name: Docker
+
+on:
+  workflow_run:
+    workflows: ["PyPI"]
+    types:
+      - completed
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+      contents: read
+      attestations: write
+      id-token: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set GOOSEBIT_VERSION env var
+        run: |
+          if [ $GITHUB_REF_TYPE = tag ]; then
+            tag=$GITHUB_REF_NAME
+          else
+            echo "This job is only supposed to be run for Git tags"
+            exit 1
+          fi
+          echo "GOOSEBIT_VERSION=${tag#v}" >> $GITHUB_ENV
+
+      - name: Log in to Docker Hub
+        uses: docker/[email protected]
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/[email protected]
+        with:
+          images: upstreamdata/goosebit
+
+      - name: Build and push Docker image
+        id: push
+        uses: docker/[email protected]
+        with:
+          context: docker
+          build-args: GOOSEBIT_VERSION=${{ env.GOOSEBIT_VERSION }}
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+
+      - name: Generate artifact attestation
+        uses: actions/attest-build-provenance@v1
+        with:
+          subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}
+          subject-digest: ${{ steps.push.outputs.digest }}
+          push-to-registry: true