Add support for grpc-web

[robsonmeemo]

trafficstars

Add a support to talk to grpc-web based services.

[augi]

It would be still great to have support for gRPC-Web in grpcurl. I'm using grpcurl to quickly test/check a gRPC services so it would be absolutely great if I could use the same tool also for gRPC-Web services 🙏

[loeffel-io]

+1