feat: implemented Mediator and added dialog service

WotBlitzStatisticsPro.Blazor/Messages/OpenSearchDialogMessage.cs

@@ -0,0 +1,15 @@
+using MediatR;
+using WotBlitzStatisticsPro.Blazor.Model;
+
+namespace WotBlitzStatisticsPro.Blazor.Messages
+{
+    public class OpenSearchDialogMessage: INotification
+    {
+        public DialogType Type { get; }
+
+        public OpenSearchDialogMessage(DialogType type)
+        {
+            Type = type;
+        }
+    }
+}