Self-Hosted Paid Signup
## Problem
As a user, when I signup for a paid package, the process is convoluted, complex and confusing. I don't understand why I have to create 2 accounts in order to signup. I would rather try to figure out how to use the product for free rather than invest my time trying to figure out how to pay.
## Solution
Move paid signup into the self hosted instance.
#### Proposal
 
#### Goals
* At signup the user should never know that a second application exists that manages their trial
* The user should not have to create a password or profile for customers.gitlab.com
* The user should be able to log into customers.gitlab.com using a code that is texted to their phone (rather than password)
* The user should be able to log into customers.gitlab.com using a code that is emailed to their address (rather than password)
* If the user is a part of this test, when linked to customers.gitlab.com from their instance, they should be taken to a signup page that does not prompt them for a password
* The user should never have to manage a trial license key
* If the instance is in a firewall that cannot reach customers.gitlab.com, the plan selection should prompt the user to contact sales
* Users should be able to spin up the instance to ensure that it never reaches out to contact customers.gitlab.com
* Additional admins on paid accounts added to the instance should have to provide their phone number and we should create a customers.gitlab.com account so that they can manage the plan for their instance
epic