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/0514-Add-getMainThreadExecutor-to-BukkitScheduler.patch

@@ -1,26 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Aleksander Jagiello <themolkapl@gmail.com>
-Date: Sun, 24 Jan 2021 22:17:54 +0100
-Subject: [PATCH] Add getMainThreadExecutor to BukkitScheduler
-
-
-diff --git a/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java b/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java
-index 71a147df3bcbd5bb82934da3e6e14326746cf2e3..e85b9bb3f9c225d289a4959921970b9963881199 100644
---- a/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java
-+++ b/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java
-@@ -653,4 +653,15 @@ public class CraftScheduler implements BukkitScheduler {
-     public BukkitTask runTaskTimerAsynchronously(Plugin plugin, BukkitRunnable task, long delay, long period) throws IllegalArgumentException {
-         throw new UnsupportedOperationException("Use BukkitRunnable#runTaskTimerAsynchronously(Plugin, long, long)");
-     }
-+
-+    // Paper start - add getMainThreadExecutor
-+    @Override
-+    public Executor getMainThreadExecutor(Plugin plugin) {
-+        Preconditions.checkArgument(plugin != null, "Plugin cannot be null");
-+        return command -> {
-+            Preconditions.checkArgument(command != null, "Command cannot be null");
-+            this.runTask(plugin, command);
-+        };
-+    }
-+    // Paper end
- }