Add missing file

BTCPayServer/Extensions/WebHostExtensions.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using BTCPayServer.Hosting;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Microsoft.AspNetCore.Hosting
+{
+    public static class WebHostExtensions
+    {
+        public static async Task StartWithTasksAsync(this IWebHost webHost, CancellationToken cancellationToken = default)
+        {
+            // Load all tasks from DI
+            var startupTasks = webHost.Services.GetServices<IStartupTask>();
+
+            // Execute all the tasks
+            foreach (var startupTask in startupTasks)
+            {
+                await startupTask.ExecuteAsync(cancellationToken).ConfigureAwait(false);
+            }
+
+            // Start the tasks as normal
+            await webHost.StartAsync(cancellationToken).ConfigureAwait(false);
+        }
+    }
+}