[web] Add dev-only button to log out secondary device

Summary:
Added a dev-only button to perform secondary device logout, for test purposes.
I deliberately did not include any checks if given device is primary or secondary, to test the hook behavior from previous diff.
In the future, logout button behavior will depend on whether current device is primary.

Depends on D12222

Test Plan: Pressed the button and repeated test plan from D12221 to check hook behavior.

Reviewers: kamil, marcin, varun

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12223