The 'Cost' price should be displayed in the main form view of
`product.product`, not only the simplified view.
The reason is that the field `product_variant_count` has the same value
for the product and the template, therefore it cannot be used to make
the distinction between the two models.
To do so, we need to reintroduce the `is_product_variant` field to make
the distinction between `product.product` and `product.template`.
opw-1814973
Nicolas Martinelli
7e724f96c5