consolidate Service interface and implementation classes

Oqtane.Client/Services/SiteTemplateService.cs

@@ -8,6 +8,18 @@ using Oqtane.Documentation;
 
 namespace Oqtane.Services
 {
+    /// <summary>
+    /// Service to retrieve <see cref="SiteTemplate"/> entries
+    /// </summary>
+    public interface ISiteTemplateService
+    {
+        /// <summary>
+        /// Returns a list of site templates
+        /// </summary>
+        /// <returns></returns>
+        Task<List<SiteTemplate>> GetSiteTemplatesAsync();
+    }
+
     [PrivateApi("Don't show in the documentation, as everything should use the Interface")]
     public class SiteTemplateService : ServiceBase, ISiteTemplateService
     {