IDFA iOS14 returns denied without displaying auth popup

In iOS 15 it could be requested with ATTrackingManager.requestTrackingAuthorization ONLY if application state is already active, so should be moved from didFinishLaunchingWithOptions to applicationDidBecomeActive

There's an option "Allow Apps to Request to Track" in system's Settings app, and if it's off, requestTrackingAuthorization will return .denied immediately.