Dynamically fill appAuthRedirectScheme

## Documentation Feedback

Is there any way to fill appAuthRedirectScheme in app/build.gradle dynamically? I want to send this string from react-native (from component, redux or etc)

```
android {
defaultConfig {
manifestPlaceholders = [
appAuthRedirectScheme: {string-which-I-initialized-on-my-component}
]
}
}

```

Start with the app/build.gradle manifestPlaceholders example and review how appAuthRedirectScheme is currently configured for the React Native app. Determine whether a value can be supplied from a component or Redux at runtime, then document the supported approach or clearly state the limitation.

索引モデルが issue の本文から書いたものです。