Separate "thank you" messages from general ads (#25867)

* Separated "thank you" messages from general ads

* Moved MessagePackPrototype to shared, cleaned up AdvertiseComponent, and actually killed AdvertisementsPackPrototype.
+More suggests changes.

* Rename PackPrototypeID to Pack in both components.

Content.Shared/Advertise/MessagePackPrototype.cs

@@ -0,0 +1,14 @@
+using Robust.Shared.Prototypes;
+
+namespace Content.Shared.Advertise;
+
+[Serializable, Prototype("messagePack")]
+public sealed partial class MessagePackPrototype : IPrototype
+{
+    [ViewVariables]
+    [IdDataField]
+    public string ID { get; private set; } = default!;
+
+    [DataField]
+    public List<LocId> Messages { get; private set; } = [];
+}