[Tunnelbroker] add message to set Device Token with Platform
Summary:
ENG-8903.
Adding a new message type, we can't modify the previous because of backward compatibility - this makes it easier to achieve what we want.
Depends on D12911
Test Plan: Tests
Reviewers: bartek, tomek
Reviewed By: bartek
Subscribers: marcin, ashoat
Differential Revision: https://phab.comm.dev/D12937