According to spec, the SDK should be responsible for calling -[UIApplication registerForRemoteNotifications], not the user

[lawrence-forooghian]

Description

RSH3a2d says:

On event CalledActivate … If the local device does not have the necessary push details, it initiates a request to the underlying platform (or otherwise generates them).

I believe that on iOS, to "initiate a request to the underlying platform" is to call -[UIApplication registerForRemoteNotifications]. However:

• This SDK never calls that method.
• We have various pieces of documentation and example code that suggest that a user of the library needs to call this method on app startup:

  • Documentation: "Push Notifications - Device activation and subscription":

    In UIApplicationDelegate#didFinishLaunchingWithOptions, call UIApplication.shared.registerForRemoteNotifications.

    But then later on in the same article (section 2.1), it says that calling activate will:```

Activate the device for push notifications with the underlying OS or platform and obtain a unique identifier for the device as a push recipient

* [iOS push notifications tutorial, step 6](https://ably.com/tutorials/ios-push-notifications#step6-register-device-for-push) demonstrates calling this method on app startup.
* Our [push-example-ios example app](https://github.com/ably/push-example-ios) copies this pattern, [calling the method on app startup](https://github.com/ably/push-example-ios/blob/49e4f6532927979af34507f16138a6a278330dba/push-interactive-app/AppDelegate.swift#L43). 

## Next steps
* Confirm whether we believe the behaviour described by the spec to be the right one
* If so, implement it in the library and remove the call to this method from our documentation / example code (confirm that existing code that does call this method will still work fine).



┆Issue is synchronized with this [Jira Bug](https://ably.atlassian.net/browse/SDK-1503) by [Unito](https://www.unito.io)

[maratal]

Here is related issue #1159