[FR] Use order reference instead of number

[bossanova808]

https://github.com/nystudio107/craft-instantanalytics/blob/319b109a180e5b4986986bcfb69bc68ef3837bf1/src/services/Commerce.php#L51

Given Commerce now has nice, friendly order reference numbers and not just UIDs for identification (and UIDs are used as a fallback for the reference if there is no reference set by the shop owner...so order->reference will always contain the preferred data) ... it seems like this would be a better value to send to Analytics here, as it will make cross referencing this data against the actual orders much easier.

https://docs.craftcms.com/commerce/v2/orders.html#order-numbers

[chadcrowell]

+1 for order.reference