Added 'taxPortions' field to TaxedItemPrice

We've added the taxPortions field to TaxedItemPrice to be consistent and align with the tax information available on TaxedPrice. Now, you can use the taxPortions field to view the individual tax subrate amounts for (Custom) Line Items and shipping-related information on a Cart.

Changes:

• [API] Added taxPortions to TaxedItemPrice.
• [GraphQL API] Changed the TaxedItemPrice type:
  • Added the taxPortions field to the TaxedItemPrice type.

The following changes were introduced in terms of GraphQL SDL:

extend type TaxedItemPrice {
  taxPortions: [TaxPortion!]!
}