debug logging: Convert to Monolog logging
Convert all beta cluster and production logging to a pure Monolog
logging stack. The historical $wgDebugLogGroups and associated
configuration is replaced with a new set of $wmg* globals and a unified
Monolog configuration generation system implemented in logging.php.
Logging channels that should be sent to udp2log and possibly to Logstash
are defined in the new $wmgMonologChannels global array. See comments
in both logging.php and InitialiseSettings.php for a description of the
possible configuration values.
Logstash logging is controlled both by $wmgMonologChannels and the new
$wmgLogstashServers global. Log events are shipped to Logstash via
syslog UDP datagrams and can be restricted by per-channel log level
independent of the log level used for udp2log filtering.
Logstash use is initially enabled only for beta cluster and group0 wikis.
This configuration uses features from 1.26wmf1 and cannot be deployed
until they are available on all wikis (est 2015-04-14).