create GitHub Actions pipeline for docker-based builds

.github/workflows/release.yml

@@ -0,0 +1,52 @@
+name: release
+on:
+  workflow_dispatch:
+    inputs:
+      wkhtmltopdf_ref:
+        description: 'Branch/Tag to use from the wkhtmltopdf/wkhtmltopdf repository'
+        required: true
+      packaging_release:
+        description: 'Release to create in wkhtmltopdf/packaging repository'
+        required: true
+      packaging_iteration:
+        description: 'Iteration (useful for tagged releases)'
+        default: '1'
+        required: true
+
+jobs:
+  docker:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        package_target:
+          - almalinux8-aarch64
+          - almalinux8-ppc64le
+          - almalinux8-x86_64
+      fail-fast: false
+    steps:
+      - name: configure docker
+        run:  |
+          echo '{ "experimental": true }' | sudo tee /etc/docker/daemon.json
+          sudo systemctl restart docker
+      - name: checkout packaging
+        uses: actions/checkout@v2
+        with:
+          path: packaging
+      - name: checkout wkhtmltopdf with submodules
+        uses: actions/checkout@v2
+        with:
+          repository: wkhtmltopdf/wkhtmltopdf
+          path: wkhtmltopdf
+          submodules: true
+          ref: ${{ github.event.inputs.wkhtmltopdf_ref }}
+      - name: build
+        run: cd packaging && python3 ./build package-docker --clean --iteration ${{ github.event.inputs.packaging_iteration }} ${{ matrix.package_target }} ../wkhtmltopdf
+      - uses: softprops/[email protected]
+        with:
+          name: ${{ github.event.inputs.packaging_release }}
+          tag_name: ${{ github.event.inputs.packaging_release }}-${{ github.event.inputs.packaging_iteration }}
+          target_commitish: ${{ github.sha }}
+          files: "packaging/targets/wkhtmltox*.*"
+          fail_on_unmatched_files: false
+          draft: true
+          body: All packages were built and uploaded automatically as a part of [this run](${{ github.event.repository.html_url }}/actions/runs/${{ github.run_id }}), using this [wkhtmltopdf branch/tag](https://github.com/wkhtmltopdf/wkhtmltopdf/tree/${{ github.event.inputs.wkhtmltopdf_ref }}).