Add payment methods with `recurring` feature support

[rvdsteege]

From customer in internal Help Scout ticket https://secure.helpscout.net/conversation/2291715621/25842:

We have Pronamic enabled on our WordPress site and when I go to the configuration (link via Mollie), Giropay has a green check mark. But I can't select this option with Restrict Content Pro. I can select all the other options we have enabled in Pronamic.

Apparently, we didn't have a Giropay payment method in Restrict Content Pro. I've already added the gateway in https://github.com/pronamic/wp-pronamic-pay-restrict-content-pro/commit/fe192f0c39fd04bfbd15624cc5af56f56c78a48e. However, this only allows for one-off payments as we don't add recurring feature support for Giropay when registering the payment methods in the Mollie gateway:

https://github.com/pronamic/wp-pronamic-pay-mollie/blob/16a8f9a7edfc216680e72c10ab83f0b81d193fde/src/Gateway.php#L128-L205

According to the Mollie documentation at https://docs.mollie.com/payments/recurring#setting-up-the-first-payment:

The following payment methods support a first payment and are thus allowed as a value for the method parameter of a first payment: applepay bancontact belfius creditcard eps giropay ideal kbc mybank paypal sofort

Of the mentioned methods, we're currently only adding recurring feature support for the following payment methods:

1. applepay
2. creditcard
3. paypal

Additionally, we register separate payment methods with recurring payments support for these payments methods:

1. bancontact → PaymentMethods::DIRECT_DEBIT_BANCONTACT
2. ideal → PaymentMethods::DIRECT_DEBIT_IDEAL
3. sofort → PaymentMethods::DIRECT_DEBIT_SOFORT

This leaves us with some unsupported recurring payment methods:

1. belfius
2. eps
3. giropay
4. kbc
5. mybank (but we don't support this method at all)

To add support for these payment methods, we need to:

1. add recurring feature support or;
2. add separate payment methods, like we do for Bancontact, iDEAL and SOFORT.

What do you think, @remcotolsma?

[remcotolsma]

Probably related to:

• https://github.com/pronamic/wp-pronamic-pay-mollie/issues/19

[rvdsteege]

Probably related to: […]

It is, I just tested this:

• with Gravity Forms, the Giropay method results in a subscription being created,
• with Restrict Content Pro, no subscription is created with Giropay.

🤨

[remcotolsma]

Discussed yesterday with @rvdsteege at @Pronamic HQ, PR is open: https://github.com/pronamic/wp-pronamic-pay-mollie/pull/34.