this is just a matter of changing how we generate subscription IDs. they are now generated from customer AND consumer, which means they will be unique for a given customer/consumer pair - in other words, a given customer will only be able to provision a given space one time.

@alanshaw pointed out that as implemented, a space could be registered by more than one user, which would make billing pretty challenging.

I tried to write a test for this, but w3up-client and access-client go to some lengths to stop a user from registering another user's space so this is a deeper rabbithole than I'd like to go down for now.