[lib][native] Call backup restore protocol after QR auth

Summary:

• On primary device, replaced stub values with actual backup keys
• On secondary device, added a function to call backup restore protocol when received backup keys from primary device

Depends on D11345

Test Plan:

• Verified that backup keys are retrieved and sent to the secondary device
• Verified that backup data is downloaded on the secondary device

Reviewers: michal, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11346