feat: add new Notification.

src/Ursa/Controls/Notification/INotificationManager.cs

@@ -0,0 +1,14 @@
+namespace Ursa.Controls;
+
+/// <summary>
+/// Represents a notification manager that can be used to show notifications in a window or using
+/// the host operating system.
+/// </summary>
+public interface INotificationManager
+{
+    /// <summary>
+    /// Show a notification.
+    /// </summary>
+    /// <param name="notification">The notification to be displayed.</param>
+    void Show(INotification notification);
+}