CommIOSNotifications module functionality definition

Summary: This differential puts foundation for work on react-native-notifications replacement on iOS. It introduces necessary file group to XCode and introduces header file that defines notifications related API used across native code on iOS.

Test Plan: No test plan for this differential.

Reviewers: tomek, atul

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D6064