Add discount codes support within the Checkout

[pkarw]

GET /V1/carts/{cartId}/coupons
GET /V1/carts/{cartId}/coupons
PUT /V1/carts/{cartId}/coupons/{couponCode}
DELETE /V1/carts/mine/coupons

The option should be available only when config.cart.synchronize_totals is turned true

[pkarw]

Related to #691

[pkarw]

I've created the API methods:

• POST http://localhost:8080/api/cart/apply-coupon?token=att6d2m63xyxkwwahm7v4vkfxapcw3sj&coupon=ARMANI&cartId=18358
• POST http://localhost:8080/api/cart/delete-coupon?token=att6d2m63xyxkwwahm7v4vkfxapcw3sj&cartId=18358
• GET http://localhost:8080/api/cart/coupon?token=att6d2m63xyxkwwahm7v4vkfxapcw3sj&cartId=18358

The example coupon code is ARMANI (-45%)

[pkarw]

vuestorefront/vue-storefront-api@f5a3640

[pkarw]

@karolbzik will add the Microcart.vue UI controls for this

[karolbzik]

@akbarik I tried to design it in the simplest way but for all critical use scenarios.

Design for the sidebar cart with 1) already defined discount code (name + value) 2) link to add a discount code 3) discount code can be removed by clicking the closing icon.

After clicking "add a discount code" link - the form appears with a field for a discount code and a button to submit the code. After clicking "add a discount code" it returns to the first view.

[akbarkz]

@karolbzik, thanks a lot!