[client-backup] exclude non-password users
Summary: This is not a big deal because there is no SIWE user in staff, but I'll add this to make it clear that backup is not yet supported for SIWE.
Test Plan:
- Backup works and menu is visible for password users
- Backup not works and menu is not visible fo SIWE users.
Reviewers: michal, marcin, bartek
Reviewed By: michal
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D9082