[native_rust_library] update creating backup to return backupID

Summary:
ENG-9656.

We need to store backupID in the store, it's needed in e.g. ENG-9616.

Depends on D13936

Test Plan:
This is the final diff for this stack so testing this end-to-end, mostly uploading User Keys, but also getting the latest Backup Info and Uploading full backup to test if this still works.
I was testing using physical iOS and Android, and both password and wallet users.
I was confirming everything with investigating DDB content.

Reviewers: bartek, tomek

Reviewed By: bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13937