[client-backup] add local settings to store
Summary:
Allow user (for now only staff) to enable in disable automatic backup.
Toggle will be introduced in next diff.
Depends on D9003
Test Plan: Flip value and check result
Reviewers: michal, marcin, bartek, inka
Reviewed By: michal, inka
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D9010