Add support for gRPC-Web using Envoy's grpc_web filter
Add support for gRPC-Web using Envoy's grpc_web filter

For more information, please refer to
https://www.envoyproxy.io/docs/envoy/v1.9.0/configuration/http_filters/grpc_web_filter#config-http-filters-grpc-web

Thanks to @rotemtam for the original implementation with the gRPC HTTP/1.1
bridge in #1201 for making this so trivial for me to contribute!

Implements feature request #456.

datawire/ambassador,datawire/ambassador,datawire/ambassador,datawire/ambassador,datawire/ambassador