fix: coupon code invalid error message

[bartoszherba]

Description

• rework coupon code component to handle GraphQL errors

Related Issue

#957

Motivation and Context

How Has This Been Tested?

• add the product to the cart
• open the cart
• try to apply invalid coupon -> observe there are no errors in the console and the error message is verbose
• try to apply valid coupon -> observe that coupon was applied
• try to remove coupon -> observe the coupon was applied

Screenshots (if appropriate):

Types of changes

• [ x] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[sethidden]

Suggested change

	[error.value.applyCoupon] = errors;
	error.value.applyCoupon = errors;

Not sure if my suggestion is correct. Can't wrap my head around whether this is detructuring?

[bartoszherba]

Because I want to get the first element. Apply coupon is not an array and I pretty much doubt that there will be more than one error in the same time..

[sethidden]

Left some comments