Web drop in 5 - Githubissues

It's not perfect yet, but maybe you can already take a look at it @rvdsteege?

Changelog

⚠️ Removed the web SDK gateway, which functioned without origin key, manual migration to client key is required!
⚠️ Removed support for Adyen origin key, manual migration to client key is required!
⚠️ Removed support for your own Apple Pay certificate, because the benefits of using Adyen's Apple Pay certificate:
- A faster way to add Apple Pay to your integration.
- There is less configuration required.
- You get access to new features.
- Apple Pay enabled by default for your Pay by Link integration, if you have one.

Switched to Adyen web drop-in version v5.14.0.
Switched to Adyen Checkout API version v68.
The Pronamic Pay payment method is updated from the Adyen webhook notification item.

Added REST API endpoint pronamic-pay/adyen/v1/return/<<payment_id>, to handle customers who come back after payment.