[lib] refactor setting device token in keyserver-reducer to ops

Summary:
Convert logic to ops approach.

Depends on D10771

Test Plan: Refresh web app (it cause dispatching SET_DEVICE_TOKEN_SUCCESS ) and make sure state is properly set

Reviewers: inka

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10772