Enable backup restoration for SIWE users via testing buttons
Summary: This differential introduces new screen that will carry downloading backup message, signing it and using for restoration. AS of this differential backup support for SIWE will just match what we currently have for password users - backup via testing buttons. However most of the code in this stack will be reused to implement full backup-restore feature.
Test Plan:
- Sign in as SIWE
- Make drafts. Upload compaction.
- Log out.
- Sign in back.
- Restore from backup.
- Ensure drafts are back.
Reviewers: kamil, tomek, ginsu, inka, ashoat
Reviewed By: kamil, ashoat
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D12036