Add code examples for ColorSpaceMenuHelper

The [documentation provides some C++ and Python code examples](https://opencolorio.readthedocs.io/en/latest/guides/developing/developing.html) for doing various things with the OCIO API. There is a need for some examples that shows how to use the AppHelpers API which is intended to help app developers improve their user experience. The most important thing to add would be how to use the [ColorSpaceMenuHelper API ](https://github.com/AcademySoftwareFoundation/OpenColorIO/blob/87126fad7f27a703850e098a9a75e0ef206b3da9/include/OpenColorIO/OpenColorAppHelpers.h#L190)which is intended to allow applications to easily build color space menus that are filtered using attributes such as categories.

This should show how to configure the ColorSpaceMenuParameters, instantiate a ColorSpaceMenuHelper, and iterate over the resulting menu items.