Log Smarty debug to it's own channel

Log Smarty debug to it's own channel

I just wrote the docs on the right way to log using this example
https://docs.civicrm.org/dev/en/latest/framework/logging/

- so we should make it the same. I tested locally
& this results in the smarty debugging going to a separate file (good).

I personally think we should send all the IPN files off to their
own channel but am loath to be pro-active on changing that