chore: Build flatpak repos in GitHub workflow

.github/workflows/alpha.yml

@@ -580,3 +580,62 @@ jobs:
           commit_user_email: zen-browser-bot@users.noreply.github.com
           repository: ./updates-server
 
+  distro-flatpak:
+    name: Build flatpak repos
+    needs: [release]
+    runs-on: ubuntu-latest
+    if: ${{ github.event.inputs.create_release == 'true' }}
+
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          repository: zen-browser/flatpak
+          token: ${{ secrets.DEPLOY_KEY }}
+          submodules: recursive
+
+      - name: Ensure repo is on main branch
+        run: |
+          cd repo
+          git checkout main
+          git pull
+
+      - name: Install flatpak builder
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y flatpak-builder
+
+      - name: Install build dependancies
+        run: |
+          sudo flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
+          sudo flatpak install flathub org.freedesktop.Platform//22.08 org.freedesktop.Sdk//22.08 org.mozilla.firefox.BaseApp//22.08 -y
+
+      - name: Import GPG keys
+        run: |
+          mkdir ~/.gpg
+          echo -n "$GPG_SIGNING_KEY" | base64 --decode | gpg --import --homedir ~/.gpg
+        env:
+          GPG_SIGNING_KEY: ${{ secrets.GPG_SIGNING_KEY }}
+
+      - name: Download artifacts
+        uses: actions/download-artifact@v3
+        with:
+          name: zen.linux.tar.bz2
+        
+      - name: Move artifacts
+        run: |
+          mv zen.linux.tar.bz2 repo/zen.tar.bz2
+
+      - name: Build flatpak
+        run: |
+          flatpak-builder --force-clean --ccache --jobs=8 --repo=repo zen org.mozilla.firefox.BaseApp.json
+
+      - name: Sign flatpak
+        run: |
+          flatpak build-sign repo --gpg-homedir ~/.gpg --gpg-sign=${{ secrets.GPG_KEY_ID }}
+          flatpak build-update-repo repo --gpg-homedir ~/.gpg --gpg-sign=${{ secrets.GPG_KEY_ID }}
+          gpg2 --homedir ~/.gpg --export ${{ secrets.GPG_KEY_ID }} > repo/zen.gpg
+
+      - name: Upload flatpak repo
+        uses: actions/upload-artifact@v3
+        with:
+          name: zen.flatpak