[native] update action types and reducer for setting comm access token

Summary:
Added a new action type and updated the reducer so we can set the token string in redux state

Depends on D9113

Test Plan:
how i tested the SET_ACCESS_TOKEN action: https://gist.github.com/vdhanan/c1a70adc6125268a8f9a085f0b1fcea2
tested the other cases in reduceServicesAccessToken by logging out and deleting account on iOS simulator and dispatching a SET_NEW_SESSION action manually from the redux devtools (confirmed that the token was set to null in redux state in all these cases)

Reviewers: marcin, atul, ashoat

Reviewed By: marcin, ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9114