Add duration model to type helper

Author: Caitlin Bales (MSFT)

src/GraphODataTemplateWriter/CodeHelpers/Android/TypeHelperAndroid.cs

@@ -42,6 +42,8 @@ public static string GetTypeString(this OdcmType @type)
                     return "com.microsoft.graph.model.DateOnly";
                 case "TimeOfDay":
                     return "com.microsoft.graph.model.TimeOfDay";
+                case "Duration":
+                    return "javax.xml.datatype.Duration";
                 case "Json":
                     return "com.google.gson.JsonElement";
                 case "Binary":