feat(notification-outbox): add NotificationType and NotificationStatus enums

src/ScadaLink.Commons/Types/Enums/NotificationStatus.cs

@@ -0,0 +1,14 @@
+namespace ScadaLink.Commons.Types.Enums;
+
+/// <summary>
+/// Lifecycle status of a notification in the central outbox. The site-local
+/// <c>Forwarding</c> concept is intentionally not part of the central status set.
+/// </summary>
+public enum NotificationStatus
+{
+    Pending,
+    Retrying,
+    Delivered,
+    Parked,
+    Discarded
+}

src/ScadaLink.Commons/Types/Enums/NotificationType.cs

@@ -0,0 +1,9 @@
+namespace ScadaLink.Commons.Types.Enums;
+
+/// <summary>
+/// Delivery channel for a notification. Currently only email is supported.
+/// </summary>
+public enum NotificationType
+{
+    Email
+}