Expose `provisioned_by_this_group` information via API

Problem to solve:

This information is being used to add the "Enterprise" tag to users in the Group members list in !63474 (merged) (merged).

Customers would like to be able to access it via the REST or GraphQL API as apart of their user reporting process. As far as I can tell, they can only access it programmatically via web scraping which is far from ideal.