Support payload/request keys for iOS 16 live activities

[crafterm]

This PR adds support for push payload and request keys used when sending an update to an iOS 16 live activity, as per:

https://developer.apple.com/documentation/activitykit/updating-and-ending-your-live-activity-with-activitykit-push-notifications

ie:

• event
• timestamp
• content-state
• stale-date

and additionally a wrapper push_type for setting the apns-push-type request header with fallback to the existing background_notification? method when unset.

Updates to the README where required.

Confirmed working using my local project.

Thanks for your consideration - any changes or feedback require please let me know 🙏

[benubois]

Hi @crafterm,

This looks great, thank you!

The test failures are unrelated to your PR so I'm going to go ahead an merge this.

[ostinelli]

Thank you @crafterm and @benubois! Gonna push 1.7.1 soon (when we get back to green).

[crafterm]

Thanks team! 🙏