Make the new Stripe redirect url available

@Teodor @patrick
FYI the Stripe tech specialist added the following info, which may make the setup easier:

Also… as a note we recently started returning the redirect url server-side on session creation (https://stripe.com/docs/payments/accept-a-payment#redirect-customers) so you don’t even have to use stripe.redirectToCheckout anymore… you could just use that redirect url itself and this would clean things up here if you want to use that instead.

Indeed I do see the url in the session.create response.