Correct resource name for product_customization_field

[ibobo]

The resource was missing the product_ prefix.

Questions	Answers
Branch?	Documentation for 1.7.x, but the problem is present also in the docs for the 8.x and 9.x.
Description?	The page reported the resource as customization_field instead of product_customization_field.
Fixed ticket?

[ibobo]

It seems the resource is product_customization_fields but the content of the document should stay customization_field... I think there should be a special "warning" for this.