Support `/grpc` in port definitions

[cjellick]

Related: https://github.com/acorn-io/runtime/pull/2306/files

In the above PR, we introduced http2 as a protocol you can specify when defining a port. That did some backend things to make http2 and grpc work.

However, the gRPC story isn't complete. To use the URL generated by acorn as a gRPC endpoint, one must ""remove the https:// and add :443 to the end". This makes it apparent that w should support grpc as a protocol and automatically do the above when rendering the endpoint.