Returns a network bulk enrollment by its identifier. Once a feed has been registered
with this enrollment's id on POST /network-bulk-feeds, the representation carries
networkBulkFeedId and a networkBulkFeed link. An enrollment that belongs to
another account answers 404.

Requires the network-bulk-enrollments:read scope. Tokens that only hold
network-bulk-feeds:read are still accepted, so existing integrations keep working.