This handles two cases:

1. Login - this logic will be executed on the device logged in using legacy Identity auth notifying other peers.
2. Whenever becoming aware of another user - ping him to fetch our newest device list.

Note: This code will be removed in the future after fully launching secondary device auth.

Depends on D12379

1. Run local TB, and Identity, and make all clients connect to it.
2. usingCommServicesAccessToken = true
3. Login on multiple devices (2 devices of user A, 1 device of user B but A is aware of B).
4. Login on a new device of user B.
5. All A's and B's devices should receive a device list update.