[native] Sign device list during QR auth

Summary:
Updated the QR Auth flow on primary device to sign the device list update with Olm account before calling the UpdateDeviceList RPC.

Depends on D11899

Test Plan: Performed the QR Auth flow. Then called the GetDeviceListHistoryForUser RPC to check if the signature is present for the latest update.

Reviewers: kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11901