Automatically build and publish packages via Github Actions

We can currently only build for Ubuntu versions because we're not yet
publishing libzim for Debian.

Development builds (on commits to master) will build against master libzim
while release builds (on tag pushes) will build against the most recent
release of libzim.

.github/workflows/package.yml

@@ -0,0 +1,78 @@
+name: Packages
+on: [push, pull_request]
+
+jobs:
+  build-deb:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        distro: [ubuntu-groovy, ubuntu-focal, ubuntu-eoan]
+    steps:
+      - uses: actions/checkout@v2
+
+      # Determine which PPA we should upload to
+      - name: PPA
+        id: ppa
+        run: |
+          if [[ $REF == refs/tags* ]]
+          then
+            echo "::set-output name=ppa::kiwixteam/release"
+          else
+            echo "::set-output name=ppa::kiwixteam/dev"
+          fi
+        env:
+          REF: ${{ github.ref }}
+
+      - uses: legoktm/gh-action-auto-dch@master
+        with:
+          fullname: Kiwix builder
+          email: release+launchpad@kiwix.org
+          distro: ${{ matrix.distro }}
+
+      - uses: legoktm/gh-action-build-deb@ubuntu-groovy
+        if: matrix.distro == 'ubuntu-groovy'
+        name: Build package for ubuntu-groovy
+        id: build-ubuntu-groovy
+        with:
+          args: --no-sign
+          ppa: ${{ steps.ppa.outputs.ppa }}
+
+      - uses: legoktm/gh-action-build-deb@ubuntu-focal
+        if: matrix.distro == 'ubuntu-focal'
+        name: Build package for ubuntu-focal
+        id: build-ubuntu-focal
+        with:
+          args: --no-sign
+          ppa: ${{ steps.ppa.outputs.ppa }}
+
+      - uses: legoktm/gh-action-build-deb@ubuntu-eoan
+        if: matrix.distro == 'ubuntu-eoan'
+        name: Build package for ubuntu-eoan
+        id: build-ubuntu-eoan
+        with:
+          args: --no-sign
+          ppa: ${{ steps.ppa.outputs.ppa }}
+
+      - uses: actions/upload-artifact@v2
+        with:
+          name: Packages for ${{ matrix.distro }}
+          path: output
+
+      - uses: legoktm/gh-action-dput@master
+        name: Upload dev package
+        # Only upload on pushes to master
+        if: github.event_name == 'push' && github.event.ref == 'refs/heads/master' && startswith(matrix.distro, 'ubuntu-')
+        with:
+          gpg_key: ${{ secrets.LAUNCHPAD_GPG }}
+          repository: ppa:kiwixteam/dev
+          packages: output/*_source.changes
+
+      - uses: legoktm/gh-action-dput@master
+        name: Upload release package
+        # Only upload on pushes to master or tag
+        if: github.event_name == 'push' && startsWith(github.event.ref, 'refs/tags') && startswith(matrix.distro, 'ubuntu-')
+        with:
+          gpg_key: ${{ secrets.LAUNCHPAD_GPG }}
+          repository: ppa:kiwixteam/release
+          packages: output/*_source.changes
+