[commtest] Add tests for Identity device list

Summary:
Added integration tests for device list. I ended up with a single integration test that tests the following:

• Adding devices during register
• Adding devices during login
• Removing devices on logout
• Reordering devices so mobile is the primary device when possible
• Getting device list updates for another user and verifying their order

Depends on D10421

Test Plan: CommTest, CI

Reviewers: michal, kamil, varun

Reviewed By: kamil, varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10422