Add Support for Cart-Based Promotions with Minimum Quantity or Value Conditions

[lbve]

Description:
I would like to request a feature that allows creating promotions based on cart-level conditions.
Specifically, the promotion should apply if:

• The cart contains a minimum number of products, or
• The cart reaches a minimum total value (price).

This functionality should be similar to what Magento offers, where administrators can define rules that trigger discounts or special offers when these thresholds are met.

How Magento Handles This:
In Magento, this is implemented through Cart Price Rules. These rules allow store owners to set conditions such as:

• Subtotal greater than X amount
• Total quantity of items in the cart greater than Y

When these conditions are satisfied, Magento applies the configured action (e.g., percentage discount, fixed amount discount, free shipping). The rules can also include additional filters like product attributes, customer groups, and coupon codes, making them highly flexible for marketing campaigns.

Use Case:
For example, a store might want to offer:

• 10% off when the cart has at least 5 items, or
• 10% off when the cart total exceeds $100.

This feature would provide greater flexibility for marketing campaigns and improve the overall promotional capabilities of Medusa.