[identity] Make device list transactions more flexible

Summary:
I need the "transaction wrapper" to:

• Make the additional DB operation optional
• Return the resulting device list representation

Depends on D10797

Test Plan: Ran device list integration tests and seen no regressions

Reviewers: varun, michal

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10798