Implement Apple Pay

[msilvagarcia]

Depends on #61

Doc: https://docs.adyen.com/payment-methods/apple-pay/web-component

Ask Adyen to enable the merchantAccount and the domain in the new integration - once it's enabled and set you cannot change it so prepare it carefully.

You do not need to do the onValidateMerchant step - not updated in the docs yet
The configuration.merchantName and configuration.merchantIdentifier fields are needed BUT should be already in the response of the paymentMethods call. If these are not, ask Adyen from where can we get them for testing and add the 2 new configuration in the admin panel. Also provide these configurations from the backend to the frontend and if these variables are missing or incorrect show an error message at the payment method Apple Pay - depends if the component throws an error or just not showing up. (Show a warning message: The payment method is not available)
If the configurations are missing remove the apple pay from the list of available payment methods.

Validate if the component shows an error when an incompatible browser tries to render it.

In case the paymentMethods response has them both then we don't need to do all these extra validation steps. Otherwise, double check with Adyen.

The .isAvailable() can be used only for Google and Apple pay. To continue the generic way of implementation check at first if the .isAvailable() method exists for the component and if yes then use it.

The fields from (the list of payment request parameters)[https://docs.adyen.com/payment-methods/apple-pay/web-component#payment-request-data] are optional and not needed. Only the state.data is required to make the payments call.

Use onSubmit when the customer authorised the payment. When is the onSubmit triggered for the other payment methods? It's always triggered when the pay button is clicked, but since for other payment methods other than paypal, apple pay, google pay we don't use the pay button it should not be an issue.

Steps

1. Render the apple pay component based on the information above.
2. Test the payment method and since the testcafe test are still not working test cards and iDeal as well.

Example from prestashop: Adyen/adyen-prestashop#138