Add the Ability to Pass UTM Variables to the Partner Tracking Pixel

Howdy!

It would be very excellent to be able to pass UTM variables through the Partner Tracking pixel. Much like you can pick up partner cookies via the ref_only variable, if we had one for utm_only as a variable to pick up cookies set by the combination of our tracking script and utm variables in the url we could pass that for third party platforms.

Currently, the partner tracking pixel doesn't set UTM's even manually, for example the below:

http://mycoolsubdomain.ontraport.com/p?order_id=123123123&email=xxx@xxx.com&item_id_1=23&item_price_1=240&item_qty_1=1&utm_campaign=test

The same applies if you replace utm_campaign with n_campaign, l_campaign, etc.

This would open up some powerful possibilities!