[lib][web][native] Introduce commServicesAccessToken to Redux state

Summary: We'll use this to track the access token used to authenticate the client to Comm services.

Test Plan: I just tested this with Flow for now, but I'll test it more thoroughly in combination with the following diffs, and will wait to land it until then

Reviewers: kamil, varun, jon, atul

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7212