ci: add a workflow to build an APK

.github/workflows/artifact_building.yml

@@ -0,0 +1,46 @@
+name: Build APK
+
+on:
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      # Load google-services.json from the secrets
+      - name: Decode secrets
+        env:
+          GOOGLE_SERVICES: ${{ secrets.GOOGLE_SERVICES }}
+        run: |
+          echo "$GOOGLE_SERVICES" | base64 --decode > ./app/google-services.json
+
+      - name: Setup JDK
+        uses: actions/setup-java@v4
+        with:
+          distribution: "temurin"
+          java-version: "17"
+
+      # Caching is a very useful part of a CI, as a workflow is executed in a clean environment every time,
+      # this means that one would need to re-download and re-process gradle files for every run. Which is very time consuming.
+      #
+      # To avoid that, we cache the the gradle folder to reuse it later.
+      - name: Gradle cache
+        uses: gradle/actions/setup-gradle@v3
+
+      - name: Grant execute permission for gradlew
+        run: |
+          chmod +x ./gradlew
+
+      - name: Build with Gradle
+        run: ./gradlew assembleRelease --parallel
+
+      - name: Upload APK
+        uses: actions/upload-artifact@v2
+        with:
+          name: app-release.apk
+          path: app/build/outputs/apk/release/app-release-unsigned.apk
+