ZOOKEEPER-4337: Bump jetty to 9.4.43.v20210629 (avoids CVE-2021-34429)

Version 9.4.43.v20210629 is the latest available in the 9.4 series at the time of this commit.  Its release notes explicitly declare "This release resolves CVE-2021-34429":

  https://github.com/eclipse/jetty.project/releases/tag/jetty-9.4.43.v20210629

Author: Damien Diederen <ddiederen@apache.org>

Reviewers: Norbert Kalmar <nkalmar@apache.org>, Enrico Olivelli <eolivelli@apache.org>

Closes #1734 from ztzg/ZOOKEEPER-4337-owasp-failures

pom.xml

@@ -468,7 +468,7 @@
     <hamcrest.version>2.2</hamcrest.version>
     <commons-cli.version>1.4</commons-cli.version>
     <netty.version>4.1.63.Final</netty.version>
-    <jetty.version>9.4.39.v20210325</jetty.version>
+    <jetty.version>9.4.43.v20210629</jetty.version>
     <jackson.version>2.10.5.1</jackson.version>
     <jline.version>2.14.6</jline.version>
     <snappy.version>1.1.7.7</snappy.version>