[identity] Refactor DDB transactions to accept signatures

Summary:
Decided to refactor the closure return type in transact_update_devicelist().
The tuple is a bit ugly and could get even uglier when adding more stuff (device list signatures here). Introduced UpdateOperationInfo struct instead with a simple builder pattern. Included the signatures as well.

Depends on D11898

Test Plan: Device list unit and integration tests. Verified that signatures are stored in DDB when calling the update RPC

Reviewers: kamil, will

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11899