Amended registration of health check scheduled notifiers (email and Slack) to use a resolver method and allow others to be added without modifying core

src/Umbraco.Web/HealthCheck/HealthCheckNotificationMethodAttribute.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace Umbraco.Web.HealthCheck
+{
+    /// <summary>
+    /// Metadata attribute for health check notification methods
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
+    public sealed class HealthCheckNotificationMethodAttribute : Attribute
+    {        
+        public HealthCheckNotificationMethodAttribute(string alias)
+        {
+            Alias = alias;
+        }
+
+        public string Alias { get; private set; }
+    }
+}