Add Galoshes slowdown over slippery surfaces (#30967)

* first draft

* Fixed it all, just need to rename stuff

* Rename and add comments

* Clean-up

* Access added

Content.Shared/Slippery/SlowedOverSlipperyComponent.cs

@@ -0,0 +1,13 @@
+using Robust.Shared.GameStates;
+
+namespace Content.Shared.Slippery;
+
+/// <summary>
+/// Slows down the user when passing over an entity with <see cref="SlipperyComponent"/>. Does not prevent slipping, see <see cref="NoSlipComponent"/>.
+/// </summary>
+[RegisterComponent, NetworkedComponent, AutoGenerateComponentState, Access(typeof(SlipperySystem))]
+public sealed partial class SlowedOverSlipperyComponent : Component
+{
+    [DataField(required: true), AutoNetworkedField]
+    public float SlowdownModifier = 1f;
+}