Feature/2624848 event system watchdog entry

[ndf]

https://www.drupal.org/node/2624848

Thisi s pull-request for discussion. Sitting now with klausi

[ndf]

Whats in it:

• a logger-service (Drupal\rules\Logger\RulesLog) that dispatches any log-item in the system as an event.
• an event-type (Drupal\rules\Event\SystemLoggerEvent) with event_name 'rules_system_logger_event'
• Kernel test
• [not working] Integration test

Plz have discussions about the logger-event format.

Currently it is implemented the same as dblog.
This means that the event-subject looks like this:
$subject = array(
'uid' => $context['uid'],
'type' => Unicode::substr($context['channel'], 0, 64),
'message' => $message,
'variables' => serialize($message_placeholders),
'severity' => $level,
'link' => $context['link'],
'location' => $context['request_uri'],
'referer' => $context['referer'],
'hostname' => Unicode::substr($context['ip'], 0, 128),
'timestamp' => $context['timestamp'],
);
Tests for this format are not written yet.

[klausi]

Can you add var docs for the data type?

[klausi]

Use $this->container->get('logger.factory')->get('rules_test');

[klausi]

continued in #314