[native] add local crate to gRPC client Cargo project

Summary:
Use the crate path to add the local, unpublished crate to this project. We do this to reuse the previously-defined PAKE types

Depends on D4783

Test Plan: cargo build

Reviewers: tomek, karol

Reviewed By: tomek

Subscribers: ashoat, adrian, atul, abosh

Differential Revision: https://phab.comm.dev/D4784