Refactor `Push#requestPermission` Method to Support Both iOS and Android

[ttypic]

The current Push#requestPermission method has several major issues:

1. It only works for iOS and lacks support for Android.
2. It requires the Ably client to be initialized, which is not ideal for a simple permission request.
3. The API doesn’t support retrieving information if permission is permanently denied, or showing the permission rationale widget flag

Proposed Solution:

• Move the requestPermission method out of the Push object and into a separate PushUtils class as a static method.
• Implement cross-platform support for both iOS and Android, ensuring permission requests can be handled universally without needing to initialize the Ably client.

┆Issue is synchronized with this Jira Story by Unito