Import currency with a config action

Here's an example recipe.yml file I've been using along with the proposed MR to define a currency by simply applying the recipe and providing the required input.

name: 'Commerce Kickstart Currency'
description: 'Allows importing user-selected currency'
type: 'Commerce Kickstart'
install:
  - commerce_price
input:
  currency:
    data_type: string
    description: 'Main currency. You can add other currencies later'
    constraints:
      # todo: Add currency constraint.
      NotBlank: []
    prompt:
      method: ask
      arguments:
        question: "Enter the currency you want to install on your site. The currency must be in 3-letter format, ex. USD, EUR, or PLN"
    form:
      '#type': 'select'
      '#title': 'Currency'
      '#description': "Enter the currency you want to install on your site. The currency must be in 3-letter format, ex. USD, EUR, or PLN"
      # todo: Add options callback.
    default:
      source: value
      value: 'USD'

config:
  actions:
    commerce_price.commerce_currency.XYZ:
      currencyImport: ${currency}