Does gRPC-go URL encode `/`'s from xDS dial target

[arvindbr8]

This PR to gRFC A47 - xDS Federation , raised a question on how gRPC-go does URL encoding of /'s. It seems like we do URL encoding of the path "excluding the slashes" intentionally here.

The expected behavior is that we URL encode everything (including the /'s) from the URI path.

This issue is to track this investigation. We need to add a test case, if we don't have one.

[arvindbr8]

Ever since fc0aa46 we have been encoding gRPC Dial targets (/ inclusive).

xDS targets uses the default behavior which is to encode the path component here. https://github.com/grpc/grpc-go/blame/master/clientconn.go#L1871