Fix duplicate mech footstep sounds (#12972)

* Fix duplicate mech footstep sounds

We just add a new component for relay targets so we can use that for audio prediction.

* Fix cwash

* woop

Content.Shared/Movement/Components/MovementRelayTargetComponent.cs

@@ -0,0 +1,12 @@
+using Robust.Shared.GameStates;
+
+namespace Content.Shared.Movement.Components;
+
+[RegisterComponent, NetworkedComponent]
+public sealed class MovementRelayTargetComponent : Component
+{
+    /// <summary>
+    /// Entities that are relaying to us.
+    /// </summary>
+    [ViewVariables] public readonly List<EntityUid> Entities = new();
+}