Medusa Promotions API
A promotion discounts an amount or percentage off a cart's items, shipping methods, or the entire order. Promotions have different types, such as a `standard` promotion that just discounts an amount, or a `buyget` promotion to enforce a "buy X get Y" promotion. A promotion has rules to restrict how and when they're applied. Promotions belong to a campaign, which sets conditions on the promotion such as when it starts and ends. These API routes allow admin users to manage promotions.