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/0532-Expose-protocol-version.patch

@@ -0,0 +1,22 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Nassim Jahnke <nassim@njahnke.dev>
+Date: Fri, 26 Mar 2021 11:23:17 +0100
+Subject: [PATCH] Expose protocol version
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java b/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
+index b928b3550bc74fd91c6762bc025a0bf6c766541b..44b0acb82f10a35bc0c42fdb6fd685aadc76d789 100644
+--- a/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
++++ b/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
+@@ -550,6 +550,11 @@ public final class CraftMagicNumbers implements UnsafeValues {
+     public io.papermc.paper.inventory.ItemRarity getItemStackRarity(org.bukkit.inventory.ItemStack itemStack) {
+         return io.papermc.paper.inventory.ItemRarity.values()[getItem(itemStack.getType()).getRarity(CraftItemStack.asNMSCopy(itemStack)).ordinal()];
+     }
++
++    @Override
++    public int getProtocolVersion() {
++        return net.minecraft.SharedConstants.getCurrentVersion().getProtocolVersion();
++    }
+     // Paper end
+ 
+     /**