Add multipart machines system (#35969)

Content.Shared/Machines/Components/MultipartMachinePartComponent.cs

@@ -0,0 +1,17 @@
+using Robust.Shared.GameStates;
+
+namespace Content.Shared.Machines.Components;
+
+/// <summary>
+/// Component for marking entities as part of a multipart machine.
+/// </summary>
+[RegisterComponent, NetworkedComponent, AutoGenerateComponentState]
+public sealed partial class MultipartMachinePartComponent : Component
+{
+    /// <summary>
+    /// Links to the entity which holds the MultipartMachineComponent.
+    /// Useful so that entities that know which machine they are a part of.
+    /// </summary>
+    [DataField, AutoNetworkedField]
+    public EntityUid? Master = null;
+}