Add AppcuesNotificationService package

[mmaatttt]

Creates the AppcuesNotificationService package and updates the cocoapods example app to have a Notification Service Extension that uses AppcuesNotificationService for rich notifications (ie with image).

Cocoapods build 119 is off of this branch.

As the docs/example shows, usage is quite simple:

// In your Notification Service Extension
import AppcuesNotificationService
class NotificationService: AppcuesNotificationServiceExtension {}

(also sc-60926)

Next

• I'll also add some options for people who need other customization for push (ie something that can be called from within didReceive.
• Update the release script to release this new package as well. The version number will be synced to to main SDK version.

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #60935: update CI/CD for notification service extension.