As user I want to prevent my promotion from stacking with other promotions of the same type

[brendan-shea-pm]

Users should be able to select an option so that their promotion doesn't stack with other promotions of the same type

On an Order type promotion, doesn't stack with other Order type promotions
On an Item type promotion, doesn't stack with other Item type promotions on the same ITEM
On a Shipping type promotion, doesn't stack with a Shipping type promotion on the same SHIPPING METHOD

• Don't Stack with Same Type is the first option in the Promotions Stackability dropdown (because it is the most common use case)
• [ ]User can select a "Don't Stack with Same Type" option in the Promotions Stackability dropdown

Mockups: https://www.figma.com/file/vWot2cXXgjcsLpMq4SAX90/Kinetic?node-id=2020%3A54523&t=1V1WoiSZtKNg1OGy-0

[brent-hoover]

@vannguyenn I confirmed with Brian that this is already supported in the backend so we just need to add the additional option in the dropdown

[vannguyenn]

Thanks @zenweasel I will check this out