Support Windows named pipes

[cowwoc]

Is your feature request related to a problem?

Docker uses grpc, but on Windows we need to connect over named pipes (npipe) instead of unix pipes.

Describe the solution you'd like

I've got a java.nio.channels.SelectableChannel implementation of named pipes that does not require the use of JNI. How would I go about constructing a ManagedChannel over a named pipe instead of over a TCP connection?

This issue is related to #12013

[cowwoc]

I'm trying to get this added directly into Netty but they have yet to reply: netty/netty#15019