Reduce vendor thank you message spam and add variety (#23746)

* Moved vendor thank you messages into AdvertisementPack, making them vendor-specific.
Wrote a few example messages.

* Only display thank yous when closing the UI after a purchase.

* Tweaked a few messages

* More custom messages

* Missed one

Content.Server/Advertisements/AdvertisementsPackPrototype.cs

@@ -11,5 +11,8 @@ namespace Content.Server.Advertisements
 
         [DataField("advertisements")]
         public List<string> Advertisements { get; private set; } = new();
+
+        [DataField("thankyous")]
+        public List<string> ThankYous { get; private set; } = new();
     }
 }