[hotfix][runtime] Adds debug logs for FinalRequestProcessor to CI run

org.apache.zookeeper.server.FinalRequestProcessor provides debug logs for actual
operations being performed on the server, which might be interesting to see
when investigating test instabilities.

The following logs are part of the debug logs:
Processing request:: sessionid:0x1003757ccd40000 type:getData cxid:0x11 zxid:0xfffffffffffffffe txntype:unknown reqpath:/flink/default/checkpoint_id_counter

...contains the type of request (e.g. 'getData') and path (e.g. '/flink/default/checkpoint_id_counter').

tools/ci/log4j.properties

@@ -61,6 +61,11 @@ logger.zookeeper.name = org.apache.zookeeper
 logger.zookeeper.level = INFO
 logger.zookeeper.additivity = false
 logger.zookeeper.appenderRef.zk.ref = ZooKeeperServerAppender
+# FinalRequestProcessor in DEBUG mode enables us to see requests being processed by the ZK server
+logger.zookeeper_FinalRequestProcessor.name = org.apache.zookeeper.server.FinalRequestProcessor
+logger.zookeeper_FinalRequestProcessor.level = DEBUG
+logger.zookeeper_FinalRequestProcessor.additivity = false
+logger.zookeeper_FinalRequestProcessor.appenderRef.zk.ref = ZooKeeperServerAppender
 logger.shaded_zookeeper.name = org.apache.flink.shaded.zookeeper3
 logger.shaded_zookeeper.level = INFO
 logger.shaded_zookeeper.additivity = false