[Commerce] Update Products/Variations to refer to the different integration methods

[Mark-H]

This page is not very helpful at the moment: https://docs.modmore.com/en/Commerce/v1/Products/Variations.html

[Mark-H]

There are different integration paths at that point depending on what you sell and how.
- The "Resource Product" gets the product information (price, sku, stock etc) from TVs
- The "Products TV" gives you a one-dimensional list of products (/product variations)
- The "Products Matrix" gives you a table consisting of 2 attributes, each combination of which is a unique product.

Useful to also add to https://docs.modmore.com/en/Commerce/v1/Product_Catalog/index.html and https://docs.modmore.com/en/Commerce/v1/Getting_Started/Product_Catalog.html