Add woocommerce_review_order_before_submit position

Hi! First of all, we really appreciate your plugin. Thank you so much for it.

It would be great if you could add wocommerce_review_order_after_submit to the selection which works great for us. Currently, I just manipulate the admin page HTML to get it to work but I thought I post this as a suggestion. Maybe you could also enable a custom text field as another option.

Thanks so much and all the best