Move billing address collection to checkout step (customers.gitlab.com)

Problem

as a user, I need to provide WAY too much information before registering for customers.gitlab.com. Why do you need my address before I have even registered for an account?

Proposal

Only collect billing address at checkout

Requirements

1. A user should never have to enter their address in order to register for customers.gitlab.com. Including on the following registration, signup
2. Align receipt with updated .com checkout design
3. Users checking out after syncing their gitlab.com account should not fail to proceed on this page because address is not completed (normally users would see an error message here before they are able to checkout)
4. Adding billing address updates the users account in https://customers.gitlab.com/customers/edit
5. Credit card input is done via Zuora iframe