Creating a custom products table

[louwie17]

Description

In #5, we created a rest endpoint for products and saved them using update_option, this is not sustainable when handling hundreds/thousands of products, instead we should create our own table for our plugin to handle products.

How to create a custom table can be seen here: https://codex.wordpress.org/Creating_Tables_with_Plugins
We can then make use of $wpdb to retrieve products and make use of this in our REST endpoint.

For now we should only make the id indexed, although suggestions are welcome here.

As part of this issue it might be worth going through an SQL tutorial if you are not as familiar with SQL, here is a simple tutorial from W3Schools -> https://www.w3schools.com/sql/sql_intro.asp, but any other would suffice as well.