[Tunnelbroker] Authenticate connecting devices

Summary:
When a device starts a session with tunnelbroker, verify
the device before continuing the session.

https://linear.app/comm/issue/ENG-3977

Depends on D8916

Test Plan:

• Start identity service, tunnelbroker

cd services/commtest
cargo test --test identity_tunnelbroker_tests

Should see logs in tunnelbroker that the device was autheticated successfully

Reviewers: bartek, varun, jon, michal

Reviewed By: bartek, michal

Subscribers: michal, ashoat, tomek

Differential Revision: https://phab.comm.dev/D8918