Send transaction type for donations and verified certificates

[ECOM-543](https://openedx.atlassian.net/browse/ECOM-543): Donations analytics

Reviewers: @dianakhuang @stephensanchez 
Wondering if it's worth sending back no extra data if the slug is neither professional or verified, if something is added later, this would mistakenly add verified? Just a thought, not a big deal either way.