[native] upload User Keys backup when user is staff

Summary:
Part of ENG-9604 but only for staff.

This is also needed for ENG-9711.

Depends on D14056

Test Plan:

1. Check if backup is uploaded when user has no backup
2. Log out/in and check if backup is uploaded

Reviewers: bartek, tomek

Reviewed By: bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D14059