Issue #3362297 Provide new configuration option in the Registrant Settings form to enable/disabled the email notifications queue

• New option in the Registrant form (/admin/structure/events/registrant/settings) to enable/disable the email notifications queue:
• If enabled, the email notifications corresponding to the types below will be queued, otherwise they will be sent immediately: -- Instance Deletion Notification -- Series Deletion Notification -- Instance Modification Notification -- Series Modification Notification -- Registration Reminder