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/0558-Add-environment-variable-to-disable-server-gui.patch

@@ -1,18 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Riley Park <rileysebastianpark@gmail.com>
-Date: Mon, 17 May 2021 00:34:55 -0700
-Subject: [PATCH] Add environment variable to disable server gui
-
-
-diff --git a/src/main/java/net/minecraft/server/Main.java b/src/main/java/net/minecraft/server/Main.java
-index a99fddc55bf125fe6de7be254e9f9384c2bf9ba3..7a5e70c99716273d04f4cd28d80a38f6f6b3868e 100644
---- a/src/main/java/net/minecraft/server/Main.java
-+++ b/src/main/java/net/minecraft/server/Main.java
-@@ -325,6 +325,7 @@ public class Main {
-                 */
-                 boolean flag1 = !optionset.has("nogui") && !optionset.nonOptionArguments().contains("nogui");
- 
-+                if(!Boolean.parseBoolean(System.getenv().getOrDefault("PAPER_DISABLE_SERVER_GUI", String.valueOf(false)))) // Paper - Add environment variable to disable server gui
-                 if (flag1 && !GraphicsEnvironment.isHeadless()) {
-                     dedicatedserver1.showGui();
-                 }