grpc-transcode only supports short connection, not grpc-stream, hope to add grpc-stream support

[tx991020]

Issue description

Minimal test code / Steps to reproduce the issue

1. service Say {
   // function which can be called
   rpc Send (SayRequest) returns (SayResponse);
   // we specify that we return a stream
   rpc SendStream(SayRequest) returns (stream SayResponse);
   // taking a stream as request
   rpc ReceiveStream(stream SayRequest) returns (SayResponse);
   // takes a stream and returns stream
   rpc Bidirectional(stream SayRequest) returns (stream SayResponse);
   }

grpc 有四种模式， 现在 grpc-transcode 只支持第一种短链接， 希望 grpc-transcode 支持grpc-stream， 我在网上查了下，需要把grpc-stream 转成websocket, 然后前端才能http和grpc-stream通信