* Move code and components for live email notifications with
    post-filtering to legacy modules
  * Deprecate configuration method related that check if prefiltering is
    enabled as it's now the standard
  * Remove the configuration from xwiki.properties to turn off
    prefiltering
  * Move deprecated NotificationManager to legacy
  * Move the API NotificationConfiguration#isEventPrefilteringEnabled to legacy and every implementations relying on it too

Co-authored-by: Thomas Mortagne <thomas.mortagne@xwiki.com>