Add support for iOS provideAppNotificationSettings

[BarryCarlyon]

This is supported in the react native "version" of this library.

So rather than rehash the issue I'll just link to theirs for easy reference

invertase/react-native-firebase#5972

Please add support for providesAppNotificationSettings as documented on https://developer.apple.com/documentation/usernotifications/unnotificationsettings/2990404-providesappnotificationsettings?language=objc

So that we can have the button in iOS Notifications settings for our apps and easily open a relevant view in our apps.

[nilsabdi]

This would be a great addition!