ZOOKEEPER-4209: Update Netty to 4.1.59.Final

Update Netty to 4.1.59.Final on to address the vulnerability described at https://snyk.io/vuln/SNYK-JAVA-IONETTY-1020439

Author: Frederiko Costa <frederiko@gmail.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Damien Diederen <ddiederen@apache.org>

Closes #1605 from frederiko/netty-4.1.59-update

pom.xml

@@ -467,7 +467,7 @@
     <mockito.version>3.6.28</mockito.version>
     <hamcrest.version>2.2</hamcrest.version>
     <commons-cli.version>1.4</commons-cli.version>
-    <netty.version>4.1.50.Final</netty.version>
+    <netty.version>4.1.59.Final</netty.version>
     <jetty.version>9.4.35.v20201120</jetty.version>
     <jackson.version>2.10.5.1</jackson.version>
     <jline.version>2.14.6</jline.version>