Disable Netty resource leak detector by default.

proxy/src/main/java/com/velocitypowered/proxy/Velocity.java

@@ -1,5 +1,7 @@
 package com.velocitypowered.proxy;
 
+import io.netty.util.ResourceLeakDetector;
+import io.netty.util.ResourceLeakDetector.Level;
 import java.text.DecimalFormat;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -29,6 +31,12 @@ public class Velocity {
     if (System.getProperty("velocity.natives-tmpdir") != null) {
       System.setProperty("io.netty.native.workdir", System.getProperty("velocity.natives-tmpdir"));
     }
+
+    // Disable the resource leak detector by default as it reduces performance. Allow the user to
+    // override this if desired.
+    if (System.getProperty("io.netty.leakDetection.level") != null) {
+      ResourceLeakDetector.setLevel(Level.DISABLED);
+    }
   }
 
   /**