Added support for showManageSubscriptions on Storekit 2

[timbrandin]

This PR adds support for showManageSubscriptions: https://developer.apple.com/documentation/storekit/appstore/3803198-showmanagesubscriptions

• This panel is very useful for testing where one can cancel the subscription and avoid waiting for expire and additional renewals.
• This panel is very user friendly allowing users to cancel or change their subscription without going to the App Store or Settings app to find their subscription.

[andresesfm]

Is this a better way of getting the scene? I was using await UIApplication.shared.keyWindow?.windowScene on beginRefundRequest line :915

[timbrandin]

Not sure, maybe this is faster as it isn't async? But I'm not a Swift/Objective-C expert

[kyle-ssg]

I was looking around for this functionality. If I'm not mistaken this PR does not actually expose this function in iosSk2.js ?

With that being the case, it looks like people can just achieve this at the moment by doing

   const { RNIapIosSk2 } = NativeModules

   RNIapIosSk2.showManageSubscriptions().catch(() => {
      Linking.openURL('https://apps.apple.com/account/subscriptions')
    })

It's a really great option that has been introduced, well worth documenting!

[andresesfm]

Addressed your request on #2376 @kyle-ssg

[andresesfm]

released as 12.10.2

[kyle-ssg]

Amazing