Add a publish workflow

This will allow trusted publishing of Quart to PyPI. It is based on
the pallets standard rather than the standard used for other Quart
extensions.

.github/workflows/publish.yaml

@@ -0,0 +1,70 @@
+name: Publish
+on:
+  push:
+    tags:
+      - '*'
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    outputs:
+      hash: ${{ steps.hash.outputs.hash }}
+    steps:
+      - uses: actions/checkout
+      - uses: actions/setup-python
+        with:
+          python-version: '3.x'
+      - run: pip install poetry
+      - run: poetry build
+      # Generate hashes used for provenance.
+      - name: generate hash
+        id: hash
+        run: cd dist && echo "hash=$(sha256sum * | base64 -w0)" >> $GITHUB_OUTPUT
+      - uses: actions/upload-artifact
+        with:
+          path: ./dist
+
+  provenance:
+    needs: ['build']
+    permissions:
+      actions: read
+      id-token: write
+      contents: write
+    # Can't pin with hash due to how this workflow works.
+    uses: slsa-framework/slsa-github-generator/.github/workflows/generator_generic_slsa3.yml
+    with:
+      base64-subjects: ${{ needs.build.outputs.hash }}
+
+  create-release:
+    # Upload the sdist, wheels, and provenance to a GitHub release. They remain
+    # available as build artifacts for a while as well.
+    needs: ['provenance']
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/download-artifact
+      - name: create release
+        run: >
+          gh release create --draft --repo ${{ github.repository }}
+          ${{ github.ref_name }}
+          *.intoto.jsonl/* artifact/*
+        env:
+          GH_TOKEN: ${{ github.token }}
+  publish-pypi:
+    needs: ['provenance']
+    # Wait for approval before attempting to upload to PyPI. This allows reviewing the
+    # files in the draft release.
+    environment: 'publish'
+    runs-on: ubuntu-latest
+    permissions:
+      id-token: write
+    steps:
+      - uses: actions/download-artifact
+      # Try uploading to Test PyPI first, in case something fails.
+      - uses: pypa/gh-action-pypi-publish
+        with:
+          repository-url: https://test.pypi.org/legacy/
+          packages-dir: artifact/
+      - uses: pypa/gh-action-pypi-publish
+        with:
+          packages-dir: artifact/