fix: Scene loading for CMB Service (#3469)

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[MTTB-1278](https://jira.unity3d.com/browse/MTTB-1273)

## Changelog

- Fixed: #3458 stopped sending scene events directly to the CMB service.
The CMB service uses those events for managing what objects exist. This
PR puts back sending those messages.

## Testing and Documentation

- Upgraded `InScenePlacedNetworkObjectTests` to work with the CMB
Service

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## Backport

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No backport needed, only a 2.0.0 change.

Author: EmandM

com.unity.netcode.gameobjects/Runtime/SceneManagement/NetworkSceneManager.cs

@@ -1071,6 +1071,18 @@ private void SendSceneEventData(uint sceneEventId, ulong[] targetClientIds)
             var sceneEvent = SceneEventDataStore[sceneEventId];
             sceneEvent.SenderClientId = NetworkManager.LocalClientId;
 
+            // Send related message to the CMB service
+            if (NetworkManager.DistributedAuthorityMode && NetworkManager.CMBServiceConnection && HasSceneAuthority())
+            {
+                sceneEvent.TargetClientId = NetworkManager.ServerClientId;
+                var message = new SceneEventMessage
+                {
+                    EventData = sceneEvent,
+                };
+                var size = NetworkManager.ConnectionManager.SendMessage(ref message, k_DeliveryType, NetworkManager.ServerClientId);
+                NetworkManager.NetworkMetrics.TrackSceneEventSent(NetworkManager.ServerClientId, (uint)sceneEvent.SceneEventType, SceneNameFromHash(sceneEvent.SceneHash), size);
+            }
+
             // Send to each individual client to assure only the in-scene placed NetworkObjects being observed by the client
             // is serialized
             foreach (var clientId in targetClientIds)