Implement GrabPay at Checkout

[danielmx-dev]

Description

Blocked by #10100
In #10011 we explored the required work to implement GrabPay as a new payment method. This issue focuses on implementing this new Payment method in the checkout flows (focusing first in blocks checkout, then in shortcode/classic checkout).

Acceptance criteria

• GrabPay can be used to place orders when enabled.

Designs

We can use the assets from the Branding Guidelines provided by GrabPay.

Testing instructions

1. Onboard with a Singapore (SG) Stripe account.
2. Enable GrabPay in the WooPayments Settings.
3. Set SGD as your store currency.
4. Add any simple product to your cart (no subscriptions)
5. Go to Checkout.
6. Select GrabPay as your payment method.
7. Place the order, you'll be redirect to the test payment page.
8. Authorize the payment.
9. You'll be redirected to the order received page. Validate that the order received page contains the correct payment method name and icon.
10. Validate that the Order in WP Admin contains the correct payment method name.
11. Validate that the Transactions list contain the correct payment method name.

Repeat the checkout steps but fail the order instead.

• Validate that you are returned to checkout and a error message is displayed.
• Validate that the order status is changed to failed.
• Validate that the correct payment method name/icon is used where necessary.

Dev notes

• If the implementation for shortcode checkout becomes too difficult, you can create a separate ticket for it.
• Use the Proof of Concept branch as a guide https://github.com/Automattic/woocommerce-payments/compare/poc/grabpay?expand=1