Add wordpress_parent_id to nodes with parents

[shendriksza]

When generating some WooCommerce nodes (eg. product categories), a "parent" field is used for the wordpress parent category id. In this case, the parent field will be overridden by the GraphQL parent node.

This solves that issue, and when the node.parent is "undefined", wordpress_parent_id field is not generated

[pasdo501]

Thanks for that! I've gone ahead and extended your addition some more - nodes now also have wordpress_parent & wordpress_children fields, which are links to the nodes themselves, to make it easier to grab extra data when you want more than just the ID :)

[shendriksza]

Excellent work, thank you so much! Sorry I was in a bit of a rush when I made the pull request and did not consider if it could be improved

[pasdo501]

No problem at all, thank you for spotting & fixing the issue in the first place!