Make conveyors event driven (#9733)

Content.Server/Conveyor/ActiveConveyorComponent.cs

@@ -0,0 +1,10 @@
+namespace Content.Server.Conveyor;
+
+/// <summary>
+/// Used to track which conveyors are relevant in case there's a lot of them.
+/// </summary>
+[RegisterComponent]
+public sealed class ActiveConveyorComponent : Component
+{
+
+}