Create message template?

How does one create a new message template. I want to create a template about a customer's order that I can send after shipping. I don't see any way in the Message Template configuration to do this.

If you edit an exiting template there is a copy button to copy the current template to a new name like ShipmentSent.CustomerNotificationAfterShipping

But to use the template you need to edit the code and insert the sending of a message using the template

For instance the ShipmentSent.CustomerNotification notification is sent in

nopCommerce_4.10\Libraries\Nop.Services\Orders\OrderProcessingService.cs

            if (notifyCustomer)
            {
                //notify customer
                var queuedEmailIds = _workflowMessageService.SendShipmentSentCustomerNotification(shipment,
                                            order.CustomerLanguageId);

Search for ShipmentSentCustomerNotification