remove the header files after build so they don't appear in the devs' git status. also rename grpc_client -> native_rust_library and move it out of the cpp folder. we're renaming the cargo project because it will be more than a gRPC client library going forward.
Depends on D5104
Requirements of the reqwest body stream:
A stream of Result<impl Into<Vec<u8>>, impl Into<Box<dyn Error>>>