consolidate Service interface and implementation classes

Oqtane.Client/Services/SqlService.cs

@@ -6,6 +6,19 @@ using Oqtane.Documentation;
 
 namespace Oqtane.Services
 {
+    /// <summary>
+    ///  Service to execute a <see cref="SqlQuery"/> against the backend database
+    /// </summary>
+    public interface ISqlService
+    {
+        /// <summary>
+        /// Executes a sql query and returns its result
+        /// </summary>
+        /// <param name="sqlquery"></param>
+        /// <returns></returns>
+        Task<SqlQuery> ExecuteQueryAsync(SqlQuery sqlquery);
+    }
+
     [PrivateApi("Don't show in the documentation, as everything should use the Interface")]
     public class SqlService : ServiceBase, ISqlService
     {