Restored interface methods on obsolete IBackgroundTaskQueue (#19223)

* Restore interface methods on obsolete IBackgroundTaskQueue.

* Fixed typos in comment.

src/Umbraco.Infrastructure/HostedServices/IBackgroundTaskQueue.cs

@@ -9,4 +9,13 @@ namespace Umbraco.Cms.Infrastructure.HostedServices;
 [Obsolete("This has been relocated into Umbraco.Cms.Core. This definition in Umbraco.Cms.Infrastructure is scheduled for removal in Umbraco 17.")]
 public interface IBackgroundTaskQueue : Core.HostedServices.IBackgroundTaskQueue
 {
+    /// <summary>
+    ///     Enqueue a work item to be executed in the background.
+    /// </summary>
+    void QueueBackgroundWorkItem(Func<CancellationToken, Task> workItem);
+
+    /// <summary>
+    ///     Dequeue the first item on the queue.
+    /// </summary>
+    Task<Func<CancellationToken, Task>?> DequeueAsync(CancellationToken cancellationToken);
 }