Changes to automatic discounts

[phyninja]

Adds checkboxes 'Min. Cart Value' and 'Max. Discount Value' to automatic discounts. Functionality has been tested by manually creating orders on the dev environment. Some screenshots included below:

Discount configuration

Discount value: 50% Min. Cart Value: $10 Max. Discount Value: $50

High cart value - max discount applied

Cart was below min value

Cart met constraint to receive 50% off

[phyninja]

@franckc (cc @shahthepro), would you let me know if there's something I can do to help a team member review this PR, please?