[native] Upload and download logs

Summary:
Testing the backup log functionality on mobile devices. This is more concerned with the networking/websocket layer working and less with business logic. Business logic is tested in the previous diff, in commtest.

Depends on D10534

Test Plan:
Created and restored backup. Checked that there are no errors.

This was tested on iOS and Android emulators. I will also test this on physical devices before landing.

Reviewers: bartek, kamil

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10535