Bug on callbackscontroller for redirecting when finishing the checkout

[garciajordy]

https://github.com/nebulab/solidus_afterpay/blob/2a34867f92cbd3be6e28e6c85bd5204e295391a3/app/controllers/solidus_afterpay/callbacks_controller.rb#L17

Here we are using the solidus_frontend endpoint to retrieve the URL of the current state of the order, but if the client is only using the solidus_backend and have their own frontend, this will throw an error.

A solution would be to add a preference on the payment method for retrieving a custom endpoint.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It might be closed if no further activity occurs. Thank you for your contributions.