fix: Block websocket use in dedicated server builds (#3336)

<!-- Replace this block with what this PR does and why. Describe what
you'd like reviewers to know, how you applied the engineering
principles, and any interesting tradeoffs made. Delete bullet points
below that don't apply, and update the changelog section as appropriate.
-->

Ensure users are not using websockets when building dedicated game
server builds

<!-- Add short version of the JIRA ticket to the PR title (e.g. "feat:
new shiny feature [MTT-123]") -->
[MTT-11522](https://jira.unity3d.com/browse/MTT-11522)
[MTTB-613](https://jira.unity3d.com/browse/MTTB-613)

<!-- Add RFC link here if applicable. -->

## Changelog

- Fixed: Blocks trying to create a dedicated server build with a
websocket connection on Unity Transport.

## Testing and Documentation

- No tests have been added.

Author: EmandM

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -31,6 +31,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Changed
 
+- Ensured that a useful error is thrown when attempting to build a dedicated server with Unity Transport that uses websockets. (#3336)
 - Changed root in-scene placed `NetworkObject` instances now will always have either the `Distributable` permission set unless the `SessionOwner` permission is set. (#3305)
 - Changed the `DestroyObject` message to reduce the serialized message size and remove the unnecessary message field. (#3304)
 - Changed the `NetworkTimeSystem.Sync` method to use half RTT to calculate the desired local time offset as opposed to the full RTT. (#3212)

com.unity.netcode.gameobjects/Runtime/Transports/UTP/UnityTransport.cs

@@ -1668,6 +1668,21 @@ public void CreateDriver(UnityTransport transport, out NetworkDriver driver,
             }
 #endif
 
+#if UNITY_SERVER
+            if (m_ProtocolType == ProtocolType.RelayUnityTransport)
+            {
+                if (m_UseWebSockets)
+                {
+                    Debug.LogError("Transport is configured to use Websockets, but websockets are not available on server builds. Ensure that the \"Use WebSockets\" checkbox is checked under \"Unity Transport\" component.");
+                }
+
+                if (m_RelayServerData.IsWebSocket != 0)
+                {
+                    Debug.LogError("Relay server data indicates usage of WebSockets, but websockets are not available on server builds. Be sure to use \"dtls\" or \"udp\" as the connection type when creating the server data");
+                }
+            }
+#endif
+
 #if UTP_TRANSPORT_2_0_ABOVE
             if (m_UseEncryption)
             {