Allow enabling sand duping (#10191)

Because this exploit has been widely known for years and has not been fixed by Mojang, we decided that it was worth allowing people to toggle it on/off due to how easy it is to make it configurable.

It should be noted that this decision does not promise all future exploits will be configurable.

patches/server/0968-Fix-CraftMetaItem-getAttributeModifier-duplication-c.patch

@@ -0,0 +1,19 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: hyper1423 <backup8822@gmail.com>
+Date: Sun, 3 Dec 2023 07:38:09 +0900
+Subject: [PATCH] Fix CraftMetaItem#getAttributeModifier duplication check
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaItem.java b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaItem.java
+index 9137d6d56386111dfd072859df84e533580ee294..5cd0fbac267f9c69c5de4c200a95860f5c56d42e 100644
+--- a/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaItem.java
++++ b/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaItem.java
+@@ -1174,7 +1174,7 @@ class CraftMetaItem implements ItemMeta, Damageable, Repairable, BlockDataMeta {
+         Preconditions.checkNotNull(modifier, "AttributeModifier cannot be null");
+         this.checkAttributeList();
+         for (Map.Entry<Attribute, AttributeModifier> entry : this.attributeModifiers.entries()) {
+-            Preconditions.checkArgument(!entry.getValue().getUniqueId().equals(modifier.getUniqueId()), "Cannot register AttributeModifier. Modifier is already applied! %s", modifier);
++            Preconditions.checkArgument(!(entry.getValue().getUniqueId().equals(modifier.getUniqueId()) && entry.getKey() == attribute), "Cannot register AttributeModifier. Modifier is already applied! %s", modifier); // Paper
+         }
+         return this.attributeModifiers.put(attribute, modifier);
+     }