[iOS16] support live activity

[GonzaloAvilez]

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Documentation reference to Header aps-push-type -> https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/sending_notification_requests_to_apns

Documentation reference for aps payload to support live-activity ->
https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/generating_a_remote_notification#2943360

Purpose:

• add support for live-activity payload
  stale-date
content-state
timestamp
event **

• add support for live-activity header

**NOTE: To verify if correct field is event or events apple docs could have a typo error

Change Files:

notification.go -> support liveactivity header
payload/builder.go -> implenting stale-date, content-state, timestamp and event to aps payload

TEST results:

tests passed

[alefer9]

💯

[IvanTrivino]

Is it possible to do some E2E tests in an experimental env with these changes?

[GonzaloAvilez]

Is it possible to do some E2E tests in an experimental env with these changes?

@IvanTrivino iOS team are working in their side to support live activity right now. Once they get a way to receive the notification content in the app, we will test this feature via command line.
This library has a great command line tool, to fire notifications within the code.

[JoseRivera12]

LGTM!
Just a comment on naming convention.