Relates to coder/coder#13331

• Notifications sent (by receiver, notification_template)
• Notifications failed (by receiver, notification_template)
• Notifications retried (by receiver, notification_template)
• Notifications paused
• Notifications purged
• Queue operations
  • Enqueue time (delta between start of operation and accepted into db)
  • Dequeue time (delta between enqueued and dequeued)
• Receiver operations
  • Send time (response time from server, by response status)