Added preview feature configuration (#227)

app/MindWork AI Studio/Settings/DataModel/PreviewFeatures.cs

@@ -0,0 +1,11 @@
+namespace AIStudio.Settings.DataModel;
+
+public enum PreviewFeatures
+{
+    //
+    // Important: Never delete any enum value from this list.
+    // We must be able to deserialize old settings files that may contain these values.
+    //
+    PRE_WRITER_MODE_2024,
+    PRE_RAG_2024,
+}