Add e2e specs for Apple Pay and Google Pay
We currently have no specs for checking out with Apple Pay and Google Pay. This makes it harder to catch bugs and verify fixes like https://github.com/antiwork/gumroad/pull/2172.
Apple Pay and Google Pay are only properly testable on computers with real accounts and cards set up, but we can potentially mock the Stripe paymentRequest API or the PaymentRequest web API it uses internally. We call it here: https://github.com/antiwork/gumroad/blob/e6463f1dfd2c81ebc32f68d1797e649afae46039/app/javascript/components/Checkout/PaymentForm.tsx#L1040
We won't be able to test a working checkout, but if we can test selecting the option, assert what form fields exist, and assert some kind of "not available" error when clicking Pay it would be much better than nothing.