add some default types to de-duplicate similar implmentations

Pilz.Net/Api/Client/IBaseChildItemClient.cs

@@ -0,0 +1,9 @@
+using Pilz.Net.Data;
+
+namespace Pilz.Net.Api.Client;
+
+public interface IBaseChildItemClient<T> : IBaseClient<T> where T : IDataObject
+{
+    Task<IEnumerable<T>> GetAll(int parentId);
+    Task<T> Save(T item, int parentId);
+}