Refactor webhooks to remove need for gate configuration and add event

First patch, again, reminder that this is work in progress.

forgot to change the route name.

Reroll.

The sleep issue is moved to 🐛 Hardcoded sleep on webhook callback blocks processes Needs review . The patch there conflicts with this though.

This is working quite well for us, but note that it changes PaymentSdkInterface, so technically has BC breaking changes.

This is now finally in production for our client and so far is working well.

It's backwards compatible as the path stays the same, the gate query parameter just doesn't matter anymore.

I saw there's an option to use a sign, which might be a good idea, this doesn't use any data from the request but you could still at least get the system to do many possibly slow API requests.

Switched to a merge request and fixed a wrong route name there.

Automatically closed - issue fixed for 2 weeks with no activity.