Allow customisation of the trade store order confirmation emails

[luke]

@john-cussons

There really needs to be the ability to add some text to the email sent to a customer when they pre-order that allows for us to say something like “thank you for your pre-order we will advise you on when you can expect delivery”

This request was from @john-cussons (thank you) in Show which orders from the trade store are pre-orders, but I’ve split a single thread into two so we can track each request seperately