Add hostname to agent.toml of QUIC agent. (#927)

Author: jianjunz

source/agent/quic/agent.toml

@@ -52,4 +52,7 @@ minport = 0 #default: 0
 keystorePath = "./cert/certificate.pfx"
 
 # Port of QUIC agent is going to listen on. Default port for WebTransport is not defined in WebTransport spec. We will update it when it's defined.
-port = 7700 #default: 7700
+port = 7700 #default: 7700
+
+# FQDN of QUIC agent. It's included in WebTransport tokens as a part of the WebTransport URL client connects to. IP address will be included in WebTransport tokens if hostname is empty.
+hostname = ""