Allow control over HTTP connection use

[jerbob92]

We're trying to use Azure Relay to expose a service that requires NTLM authentication, NTLM authentication seems to be based on a connection level, in our tests, sending multiple requests at the same time, all of them result in a 400 error, possibly because it's starting the NTLM session on the same connction. When doing 1 NTLM negotiation/request at the same time, everything works correctly.

It would be nice to be able to configure the HTTP request handling, so that 1 incoming connection matches 1 outgoing connection in the HTTP request handling in Azure.