Create test to ensure that all `DashEvent` labels are unique

[eliasyishak]

Bad below

  clientNotification(
    label: 'client_notification',  // the labels are the same
    description: 'Notifications sent from the client',
  ),
  differentClientNotification(
    label: 'client_notification',  // the labels are the same
    description: 'Notifications sent from the client',
  ),