Add terms_of_service to consent_collection type (#757)

* Add terms_of_service to consent_collection type

See [API Docs](https://stripe.com/docs/api/checkout/sessions/create#create_checkout_session-consent_collection-terms_of_service)

* Add currency to create params

See [API Docs](https://stripe.com/docs/api/checkout/sessions/create#create_checkout_session-currency)

* Add support for BillingPortal.Session configuration

See [API Docs](https://stripe.com/docs/api/customer_portal/sessions/create?lang=cli#create_portal_session-configuration)

lib/stripe/billing_portal/session.ex

@@ -16,6 +16,7 @@ defmodule Stripe.BillingPortal.Session do
           :id => Stripe.id(),
           :object => String.t(),
           :created => Stripe.timestamp(),
+          :configuration => String.t(),
           :customer => Stripe.id() | Stripe.Customer.t(),
           :livemode => boolean(),
           :return_url => String.t(),
@@ -24,6 +25,7 @@ defmodule Stripe.BillingPortal.Session do
 
   @type create_params :: %{
           :customer => String.t(),
+          optional(:configuration) => String.t(),
           optional(:return_url) => String.t(),
           optional(:locale) => String.t()
         }
@@ -32,6 +34,7 @@ defmodule Stripe.BillingPortal.Session do
     :id,
     :object,
     :created,
+    :configuration,
     :customer,
     :livemode,
     :return_url,

lib/stripe/checkout/session.ex

@@ -128,7 +128,8 @@ defmodule Stripe.Session do
         }
 
   @type consent_collection :: %{
-          promotions: String.t()
+          promotions: String.t(),
+          terms_of_service: String.t()
         }
 
   @typedoc """
@@ -246,6 +247,7 @@ defmodule Stripe.Session do
           :success_url => String.t(),
           optional(:mode) => String.t(),
           optional(:client_reference_id) => String.t(),
+          optional(:currency) => String.t(),
           optional(:customer) => String.t(),
           optional(:customer_email) => String.t(),
           optional(:line_items) => list(line_item_data()),