Logging Capability (#53)

* Logging Capability

* Readability

* Redundant using

---------

Co-authored-by: Stephen Toub <stoub@microsoft.com>

src/ModelContextProtocol/Protocol/Messages/NotificationMethods.cs

@@ -29,4 +29,9 @@ public static class NotificationMethods
     /// Sent by the client when roots have been updated.
     /// </summary>
     public const string RootsUpdatedNotification = "notifications/roots/list_changed";
+
+    /// <summary>
+    /// Sent by the server when a log message is generated.
+    /// </summary>
+    public const string LoggingMessageNotification = "notifications/message";
 }