make legs affect movement speed with body (#12928)

Co-authored-by: DrSmugleaf <DrSmugleaf@users.noreply.github.com>

Content.Shared/Body/Components/BodyComponent.cs

@@ -21,6 +21,13 @@ public sealed class BodyComponent : Component, IDraggable
     [DataField("gibSound")]
     public SoundSpecifier GibSound = new SoundCollectionSpecifier("gib");
 
+    /// <summary>
+    /// The amount of legs required to move at full speed.
+    /// If 0, then legs do not impact speed.
+    /// </summary>
+    [DataField("requiredLegs")]
+    public int RequiredLegs;
+
     bool IDraggable.CanStartDrag(StartDragDropEvent args)
     {
         return true;