Function getLaunchNotification

getLaunchNotification(): Promise<PushNotificationGetLaunchNotificationOutput>
Returns the notification which launched your app from a terminated state. The launch notification is consumed by calls to this function and will yield a null result if:
1. It is more than once (i.e. subsequent calls will be null)
2. Another notification was opened while your app was running (either in foreground or background)
3. Your app was brought back to the foreground by some other means (e.g. user tapped the app icon)
Returns Promise<PushNotificationGetLaunchNotificationOutput>
- a promise resolving to PushNotificationMessage if there is a launch notification and null otherwise.
Throws
platform: PlatformNotSupportedError - Thrown if called against an unsupported platform. Currently, only React Native is supported by this API.

Example
```
const launchNotification = await getLaunchNotification();
```