[keyserver] Fix rust-node-addon after deprecation of --experimental-specifier-resolution=node

Summary:
Context in ENG-3059. rust-node-addon was broken by D6695, but --experimental-specifier-resolution=node is going away so we need another solution.

I got this solution from this GitHub comment.

Depends on D6783

Test Plan: Confirm I could import rust-node-addon and call methods on it from @jon's jonringer/identity-deleteuserrpc branch

Reviewers: jon, varun, max

Reviewed By: jon

Subscribers: tomek, atul, jon

Differential Revision: https://phab.comm.dev/D6784