feat: add automation for ubuntu/* branches asserting quilt patches ap…

…ply (#5622)

Perform the same steps that cloud-init daily recipe builds performs
to assert any packaging branch updates will not break daily builds
due to quilt patch apply issues.

Steps of daily build recipe reflected in this workflow:
- checkout main
- merge packaging branch topmost commit
- quilt push -a
- run unittests (via tox -e py3)
- quilt pop -a

.github/workflows/packaging-tests.yml

@@ -0,0 +1,47 @@
+name: Packaging Tests
+
+on:
+  pull_request:
+    branches:
+      - 'ubuntu/**'
+
+concurrency:
+  group: 'ci-${{ github.workflow }}-${{ github.ref }}'
+  cancel-in-progress: true
+
+defaults:
+  run:
+    shell: sh -ex {0}
+
+env:
+  RELEASE: focal
+
+jobs:
+  check-patches:
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          # Fetch all branches for merging
+          fetch-depth: 0
+      - name: Prepare dependencies
+        run: |
+          sudo DEBIAN_FRONTEND=noninteractive apt-get update
+          sudo DEBIAN_FRONTEND=noninteractive apt-get -y install tox quilt
+      - name: Setup quilt environment
+        run: |
+          echo 'QUILT_PATCHES=debian/patches' >> ~/.quiltrc
+          echo 'QUILT_SERIES=debian/patches/series' >> ~/.quiltrc
+
+      - name: 'Daily recipe: quilt patches apply successfully and tests run'
+        run: |
+          git config user.name "GitHub Actions"
+          git config user.email "actions@github.com"
+          git remote add upstream https://git.launchpad.net/cloud-init
+          git fetch upstream main
+          git checkout upstream/main
+          git merge ${{ github.sha }}
+          quilt push -a
+          tox -e py3
+          quilt pop -a