And that blog posts says:
Deployed initial version of a system for sub-products (DLC, in-app purchases, etc.). (admin only)
It's experimental. That's why you won't find it elsewhere in the FAQ.
So, it isn't currently available to the public?
Indeed not.
When will it be?
I don't know. Maybe support can tell you, but in my experience our dev team doesn't like to make promises like that
OK