Add root/admin user detection

This patch detects whether or not the server is currently executing as a privileged user and spits out a warning.
The warning serves as a sort-of PSA for newer server admins who don't understand the risks of running as root.
We've seen plenty of bad/malicious plugins hit markets, and there's been a few close-calls with exploits in the past.
Hopefully this helps mitigate some potential damage to servers, even if it is just a warning.

Co-authored-by: Noah van der Aa <ndvdaa@gmail.com>

paper-server/src/main/java/io/papermc/paper/util/ServerEnvironment.java

@@ -0,0 +1,23 @@
+package io.papermc.paper.util;
+
+import com.sun.security.auth.module.NTSystem;
+import com.sun.security.auth.module.UnixSystem;
+import java.util.Set;
+import org.apache.commons.lang.SystemUtils;
+
+public class ServerEnvironment {
+    private static final boolean RUNNING_AS_ROOT_OR_ADMIN;
+    private static final String WINDOWS_HIGH_INTEGRITY_LEVEL = "S-1-16-12288";
+
+    static {
+        if (SystemUtils.IS_OS_WINDOWS) {
+            RUNNING_AS_ROOT_OR_ADMIN = Set.of(new NTSystem().getGroupIDs()).contains(WINDOWS_HIGH_INTEGRITY_LEVEL);
+        } else {
+            RUNNING_AS_ROOT_OR_ADMIN = new UnixSystem().getUid() == 0;
+        }
+    }
+
+    public static boolean userIsRootOrAdmin() {
+        return RUNNING_AS_ROOT_OR_ADMIN;
+    }
+}