Add support for product attributes

[peterjaap]

If we could have attributes support in this extension, we could have full compatability with https://github.com/enanobots/m2-datapatchcreator (enanobots/m2-datapatchcreator#5)

[markshust]

@peterjaap that is a great module! I'll add in product attributes for sure so we can have this capability. It would be great to cross-promote these two modules as well (or merge them together into a single project).