ci: Build Android app with fastlane

Adds all the signing keys and other credentials required for a
successful production build.

Additionally, opens the door to deploying via CI.

.github/workflows/android.yml

@@ -17,8 +17,14 @@ jobs:
         with:
           distribution: temurin
           java-version: 17
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 2.6.10
+          bundler-cache: true
       - name: Build Application
         run: |
-          cd android
-          ./gradlew bundleRelease
-
+          cat SECRETS_TAR_GZ_B64 | base64 -d | tar -xz -C fastlane
+          fastlane android build
+        env:
+          SECRETS_TAR_GZ_B64: ${{ secrets.SECRETS_TAR_GZ_B64 }}