Add support for `title` and `body` objects in `aps.alert` object in APNs payloads

As discussed in #1111, it looks like there's a [new alert format](https://developer.apple.com/documentation/activitykit/starting-and-updating-live-activities-with-activitykit-push-notifications#Construct-the-payload-that-starts-a-Live-Activity) we should support.