Log entry start (identity filter)

Problem/Motivation

In line parser it would be nice to have a config for this part if the server log doesn't match this exact pattern:

    // We assume every log entry starts with "M j H:i:s hostname identity: "
    // so we remove this part before exploding the remainder.
    $fake_beginning = \date('M j H:i:s') . ' ' . \gethostname() . ' drupal: ';

For now, at least we can set the identity as the syslog config (@see patch)