consolidate Service interface and implementation classes

Oqtane.Client/Services/DatabaseService.cs

@@ -8,6 +8,18 @@ using Oqtane.Shared;
 
 namespace Oqtane.Services
 {
+    /// <summary>
+    /// Service to retrieve <see cref="Database"/> information.
+    /// </summary>
+    public interface IDatabaseService
+    {
+        /// <summary>
+        /// Returns a list of databases
+        /// </summary>
+        /// <returns></returns>
+        Task<List<Database>> GetDatabasesAsync();
+    }
+
     [PrivateApi("Don't show in the documentation, as everything should use the Interface")]
     public class DatabaseService : ServiceBase, IDatabaseService
     {