CI: Fix Docker Hub image build & push (#1100)

We tried using the auto Docker Hub thingie, but it's flaky.
Reverting to manually pushing as part of release CI.

.github/workflows/publish.yml

@@ -21,3 +21,33 @@ jobs:
     - run: npm publish
       env:
         NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
+        
+  # Docker build image and push to DockerHub
+  docker:
+    needs: build
+
+    env:
+      IMAGE_ID: ${{ secrets.DOCKERHUB_USERNAME }}/nativefier
+    
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Build image
+        run: docker build . --file Dockerfile --tag "$IMAGE_ID:latest"
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+          
+      - name: Tag and Push
+        run: |
+          # Tag docker image the commit SHA
+          docker tag "$IMAGE_ID:latest" "$IMAGE_ID:${GITHUB_SHA::8}"
+          
+          # Push the images to the registry
+          docker push "$IMAGE_ID:latest"
+          docker push "$IMAGE_ID:${GITHUB_SHA::8}"