[shared/grpc_clients] Export tonic to avoid version mismatch

Summary:
If the consuming crate has a different version, then you will
get compilation errors when mismatching the different tonic versions.
Export tonic from grpc_clients to avoid this issues.

Also explicitly state that the build.rs should be re-ran if a proto
changes.

In support of https://linear.app/comm/issue/ENG-3977

Depends on D8891

Test Plan: Applied in next diff

Reviewers: varun, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8917