NotificationReceiverController - Should use custom RouteScope so it works with headless sales channels as well

[AndreasA]

Describe the bug
With multiple sales channels the NotificationReceiverController would require a corresponding Storefront sales channel with a correct domain configuration. It will not work for headless sales channels and it might also be tricky regarding which URL to use if the sales channel has multiple or one uses the same adyen configuration for multiple sales channels.

Instead if would make more sense to either use the admin API ACL definitions with a corresponding permission
or a custom route scope defintion.
The custom route scope is probably the way to go as you can define it for the adyen prefix, and can create your own authentication which you probably need for the web hooks. It should optionally be possible to specify the sales channel ID in the URL, e.g. as query parameter or suffix.

It would probably be necessary

Versions
Shopware version: 6.4.11.1
Plugin version: 3.4.1