Backoffice Api: Server Controller (#12932)

* Add initial implementation using 1 controller pr. action

* Add OpenApiTag attribute

Otherwise the endpoints won't be grouped correctly

* Use correct response type

* Move ApiVersion to endpoint controllers

* Add ServerController suffix to endpoint controllers

(cherry picked from commit 9cf7e965a9)

src/Umbraco.Cms.ManagementApi/ViewModels/Server/ServerStatusViewModel.cs

@@ -0,0 +1,10 @@
+using System.Text.Json.Serialization;
+using Umbraco.Cms.Core;
+
+namespace Umbraco.Cms.ManagementApi.ViewModels.Server;
+
+public class ServerStatusViewModel
+{
+    [JsonConverter(typeof(JsonStringEnumConverter))]
+    public RuntimeLevel ServerStatus { get; set; }
+}