[identity] some small fixes

Summary: remove a couple clones of the database client, use tokio spawn to catch errors in streaming RPCs, remove use of unwrap

Test Plan: tested the existing RPCs and errors like client disconnects were handled more gracefully (no broken pipe errors)

Reviewers: jon, bartek, tomek

Reviewed By: jon

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6940