I have an app that uses local device only CoreData (NSPersistentContainer). I am looking to migrate so the app is compatible with NSPersistentCloudKitContainer. I understand all the CloudKit setup for NSPersistentCloudKitContainer, but how do I migrate the data that is on the player's phones to iCloud? (i.e. how do I migrate existing core data from NSPersistentContainer to NSPersistentCloudKitContainer)?