Examples added to Create a Cart and Required request parameters added

• Required parameters for all requests in V3 have been added.

• Examples of how to Create a Cart using the Server to Server API have been added.

• When using the is_visible filter on products and categories, the filter is 1 and 0. It previously listed true and false.

https://api.bigcommerce.com/stores/store_hash/v3/catalog/products?is_visible=1