fix(cpp-qt-client): add asJsonObject method to OAIEnum class (#19307) (#21211)

* add asJsonObject method to OAIEnum class to fix enum handling in query parameters

* update samples

---------

Co-authored-by: William Cheng <wing328hk@gmail.com>

samples/client/petstore/cpp-qt/client/PFXEnum.h

@@ -12,6 +12,7 @@
 #ifndef PFX_ENUM_H
 #define PFX_ENUM_H
 
+#include <QJsonObject>
 #include <QJsonValue>
 #include <QMetaType>
 #include <QString>
@@ -36,6 +37,12 @@ public:
         return jstr;
     }
 
+    virtual QJsonObject asJsonObject() const {
+        QJsonObject obj;
+        obj["value"] = jstr;
+        return obj;
+    }
+	
     virtual void fromJson(QString jsonString) {
         jstr = jsonString;
     }