[keyserver] improve error messages in rust-node-addon

Summary:
add a more detailed message in case an error is caught.

Depends on D8298

Test Plan: ran keyserver but not identity service to get errors connecting to identity. saw better error logs

Reviewers: jon, bartek

Reviewed By: jon

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8299