[client-backup] add restore test

Summary:
We can do it automatically, but I don't want to slow the app more. Result should be presented in Alert.

Depends on D9003

Test Plan:
Test both successful and failed restore.

Reviewers: michal, marcin, bartek, inka

Reviewed By: inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9004