doc(404): add not found middleware (#4615)

* doc: 增加 404 重定向

* refactor: 修复 301 重定向问题

Author: ArgoZhang

src/BootstrapBlazor.Server/Program.cs

@@ -41,6 +41,16 @@
 
 var app = builder.Build();
 
+app.UseStatusCodePages(context =>
+{
+    var response = context.HttpContext.Response;
+    if(response.StatusCode == 404)
+    {
+        response.Redirect("/", true);
+    }
+    return Task.CompletedTask;
+});
+
 // 启用本地化
 var option = app.Services.GetService<IOptions<RequestLocalizationOptions>>();
 if (option != null)