Apple: Document how to restart the SDK

[philipphofmann]

The Apple docs don't mention how to close and restart the SDK. Explain how to do this here: https://docs.sentry.io/platforms/apple/guides/ios/configuration/draining/

[sfanahata]

@philipphofmann - I don't see sentrySDK.close ( ) listed as a method in the Apple SDK. Does that need to be added in? I'm looking at the native shutdown and draining doc as an example, and that one calls this process out explicitly, which would be a great add if it applies to Apple.

[philipphofmann]

@sfanahata, yes, that needs to be added similarly to the native shutdown docs.

[kahest]

related: #13163
the above issue probably needs to fully describe what this issue covers, and more