resolves #4899: output cache for sitemap

Oqtane.Client/Services/CacheService.cs

@@ -0,0 +1,23 @@
+using System.Net.Http;
+using System.Threading;
+using System.Threading.Tasks;
+
+using Oqtane.Documentation;
+using Oqtane.Shared;
+
+namespace Oqtane.Services
+{
+    /// <inheritdoc cref="ICacheService" />
+    [PrivateApi("Don't show in the documentation, as everything should use the Interface")]
+    public class CacheService : ServiceBase, ICacheService
+    {
+        public CacheService(HttpClient http, SiteState siteState) : base(http, siteState) { }
+
+        private string ApiUrl => CreateApiUrl("Cache");
+
+        public async Task EvictOutputCacheByTag(string tag, CancellationToken cancellationToken = default)
+        {
+            await DeleteAsync($"{ApiUrl}/outputCache/evictByTag/{tag}");
+        }
+    }
+}