chore(tonic-web): include crate in top-level workspace (#648)

This PR adds the tonic-web crate to tonic's workspace members. 
Unit and integration tests should now run as part of CI runs.

tonic-web/tests/integration/src/lib.rs

@@ -1,6 +1,6 @@
 use std::pin::Pin;
 
-use tokio_stream::{self as stream, StreamExt, Stream};
+use tokio_stream::{self as stream, Stream, StreamExt};
 use tonic::{Request, Response, Status, Streaming};
 
 use pb::{test_server::Test, Input, Output};