Enable Frontend Logging in Production Environment in Symfony

1. Enable logging in frontend/config/settings.yml.
   logging_enabled: true
2. Change the code below in the prod section of the factories.yml:
   

     logger:
       class:   sfNoLogger
       param:
         level:   err
         loggers: ~
   

   with this:
   

     logger:
       class: sfAggregateLogger
       param:
         level: debug
         loggers:
           sf_web_debug:
             class: sfWebDebugLogger
             param:
               level: debug
               condition:       %SF_WEB_DEBUG%
               xdebug_logging:  true
               web_debug_class: sfWebDebug
           sf_file_debug:
             class: sfFileLogger
             param:
               level: debug
               file: %SF_LOG_DIR%/%SF_APP%_%SF_ENVIRONMENT%.log