Implement support for payments with asynchronous confirmation in checkout

[gpressutto5]

Description

In #10013 we explored the required work to implement Multibanco as a new payment method. One of the problems encountered listed in paJDYF-ged-p2 is that our gateway is not ready to handle payments with asynchronous confirmation. This is because in WC_Payment_Gateway_WCPay::update_order_status() we only return a success response when the intent is authorized, or a failure response when there’s an error. So the cart is not cleared and the customer is no correctly redirected to the thank you page when the intent still requires action.
We already have the logic to handle webhooks in place, so we only need to implement a way to finalize the order before the payment is confirmed.

Acceptance criteria

• The order is placed correctly even when the intent still requires an action.

Testing instructions

1. Use the branch from the Multibanco POC POC: Multibanco #10032
2. Enable Multibanco
3. Place an order (test blocks and shortcode checkout)
4. You should be redirected to the thank you page and the cart is clean
5. The order is created and its status is on hold.

Additional context

paJDYF-ged-p2