Allow form submission to redirect to proper URL.

When checking out, the user must click on the paypal express icon in order to complete checkout. This is a bit odd for a site where that is the only checkout option since users can click "SAVE AND CONTINUE" which just brings them back to the same screen again.

Copied from the old spree_paypal_express so not sure how correct it is, just got it to work...

It was done rather quickly but seems to work. I don't have enough involvement with this project to say for sure this is what is correct to be done or not (maybe all thats needed is to redirect_to(payment_method_id: params[:payment_method_id] ??? )