[REST client support] Code helper research spike

As described by the containing QTBUG-112276 Epic, the "code-based" approach for easing Qt REST client application development is

• Creation of general purpose REST helper classes / components / wrappers
• Help with typical REST client application needs, while remaining agnostic of any exact REST API

The goal of this task is to have an understanding:

• The main features that help in this regard, while remaining generic enough to work with most common REST use cases
• Main implementation options

Upon completion of this task, starting the of development should be possible (will still contain some research element, but the general understanding should be there).