Add log level config in pulsar-client (apache#8195)

### Motivation
When using pulsar-client CLI, we have a lot of log4j logs useless for just sending/receiving messages.
It could great to not display these logs with just a env variable (like in pulsar-admin).

### Modifications
The log level can be configured with the system property `pulsar.log.level` for the Java application.
The modification is the ability to set this level using a env variable PULSAR_LOG_LEVEL (default: info).

bin/pulsar-client

@@ -98,10 +98,12 @@ OPTS="$OPTS $PULSAR_EXTRA_OPTS"
 # log directory & file
 PULSAR_LOG_DIR=${PULSAR_LOG_DIR:-"$PULSAR_HOME/logs"}
 PULSAR_LOG_APPENDER=${PULSAR_LOG_APPENDER:-"Console"}
+PULSAR_LOG_LEVEL=${PULSAR_LOG_LEVEL:-"info"}
 
 #Configure log configuration system properties
 OPTS="$OPTS -Dpulsar.log.dir=$PULSAR_LOG_DIR"
 OPTS="$OPTS -Dpulsar.log.appender=$PULSAR_LOG_APPENDER"
+OPTS="$OPTS -Dpulsar.log.level=$PULSAR_LOG_LEVEL"
 
 #Change to PULSAR_HOME to support relative paths
 cd "$PULSAR_HOME"