Make port configurable

Author: EmandM

com.unity.netcode.gameobjects/Tests/Runtime/DistributedAuthority/DistributedAuthorityCodecTests.cs

@@ -30,9 +30,15 @@ internal class DistributedAuthorityCodecTests : NetcodeIntegrationTest
         private NetworkManager Client => m_ClientNetworkManagers[0];
 
         private string m_TransportHost = Environment.GetEnvironmentVariable("NGO_HOST") ?? "127.0.0.1";
-        private const int k_TransportPort = 7777;
+        private static readonly ushort k_TransportPort = GetPortToBind(7777);
         private const int k_ClientId = 0;
 
+        private static ushort GetPortToBind(ushort defaultPort)
+        {
+            var value = Environment.GetEnvironmentVariable("ECHO_SERVER_PORT");
+            return ushort.TryParse(value, out var configuredPort) ? configuredPort : defaultPort;
+        }
+
         private GameObject m_SpawnObject;
 
         internal class TestNetworkComponent : NetworkBehaviour