Feature/nat 212 213

This PR covers NAT-212 and NAT-213.

gso/products/product_types/__init__.py

+"""Product types define the different products that are available.
+
+Multiple product blocks may insist on a single product type. In that sense, a product type is a mode general description
+of a product. For example, the product type {class}`Device` must either be a router or a switch, both being separate
+product blocks.
+"""