[DOCS] Added documentation for log4j-extras dependency

config/logging.yml

@@ -39,6 +39,17 @@ appender:
       type: pattern
       conversionPattern: "[%d{ISO8601}][%-5p][%-25c] %m%n"
 
+  # Use the following log4j-extras RollingFileAppender to enable gzip compression of log files. 
+  # For more information see https://logging.apache.org/log4j/extras/apidocs/org/apache/log4j/rolling/RollingFileAppender.html
+  #file:
+    #type: extrasRollingFile
+    #file: ${path.logs}/elasticsearch.log.gz
+    #rollingPolicy: timeBased
+    #rollingPolicy.FileNamePattern: ${path.logs}/${cluster.name}%d{yyyy-MM-dd}.log.gz
+    #layout:
+      #type: pattern
+      #conversionPattern: "%d{ISO8601}"
+
   index_search_slow_log_file:
     type: dailyRollingFile
     file: ${path.logs}/${cluster.name}_index_search_slowlog.log

docs/reference/setup/configuration.asciidoc

@@ -319,3 +319,6 @@ Extensive information on how to customize logging and all the supported
 appenders can be found on the
 http://logging.apache.org/log4j/1.2/manual.html[log4j documentation].
 
+coming[1.5.0] Additional Appenders and other logging classes provided by 
+http://logging.apache.org/log4j/extras/[log4j-extras] are also available, 
+out of the box.