[Native] Migrate native_rust_library to use identity client stubs

Summary:
The existing bindings used the now "keyserver" API, and we
need to migrate the usage to the newer client gRPC API.

In addition, decided to update the reference of comm-opaque to use
the opaque_ke 2.0 comm-opaque2 project

https://linear.app/comm/issue/ENG-3384

Test Plan:
This will be tested thoroughly in later diffs, for now this is
intended to allow for division of work between implmenting the different RPCs

cd native/native_rust_library
cargo build

Reviewers: varun, ashoat, bartek

Reviewed By: varun

Subscribers: tomek, atul

Differential Revision: https://phab.comm.dev/D7155