[native] introduce user profile constants

Summary: Some of the constants defined in D9274 are going to be used across different files. To ensure that this code is future proof and less "brittle" I created this constants file as a single source of truth where we define and export the relevant constants

Test Plan: flow

Reviewers: atul, inka

Reviewed By: atul

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9358