Add custom app group name property

[jarrodparkes]

Description

One Line Summary

Adds a plugin property appGroupName to customize the app group name in accordance with https://documentation.onesignal.com/docs/ios-sdk-setup#use-custom-app-group-name.

Details

Motivation

Why is this code change being made? Or what is the goal of this PR?
Provide functionality expected by OneSignal's iOS SDK.

Testing

Manual testing

I tested this change with my own Expo-based application on a real device, and I was able to successfully send and receive a push notification from OneSignal.

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have personally tested this on my device, or explained why that is not possible
• I have tested this on the latest version of the plugin
• I have tested this on both Android and iOS

Final pass

• Code is as readable as possible.
• I have reviewed this PR myself, ensuring it meets each checklist item

[eaguad1337]

I just tested it and works. Thank you.
Please merge this.