Add convenience scripts for android bundle & validation

[code-jenn-or]

Consider adding scripts to package.json that help with android builds.

"android:clean": "cd android && ./gradlew clean && cd ..",
    "android:bundle": "cd android && ./gradlew app:bundleRelease && cd ..",
    "android:gen-apks": "bundletool build-apks --bundle=./android/app/build/outputs/bundle/release/app.aab --output=./bundle/myapp.apks",
    "android:install-apks": "bundletool install-apks --apks=./bundle/myapp.apks",