Introduce IContentNestedDataSerializer to allow injecting a custom serializer for nucache

src/Umbraco.Web/PublishedCache/NuCache/DataSource/IContentNestedDataSerializer.cs

@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Umbraco.Web.PublishedCache.NuCache.DataSource
+{
+    public interface IContentNestedDataSerializer
+    {
+        ContentNestedData Deserialize(string data);
+        string Serialize(ContentNestedData nestedData);
+    }
+}