[Comm-opaque2] Add grpc helper for wrapped protocol error

Summary:
Provide utilities for dealing with errors with our
wrapped error type.

Depends on D7198

Test Plan:
Will be used in later diffs.

cd shared/comm-opaque2
cargo build

Reviewers: varun, bartek

Reviewed By: varun

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7200