Require a credit card before using shared runners on GitLab.com for Free

Overview

Using shared runners on GitLab.com is a great way to get started with CI. Now that we're adding the benefit of add-on runner minutes, we should consider the business impact of requiring that free users provide GitLab with a credit card before they're able to use shared runners.

Proposal

• Before a user is able to run a pipeline on GitLab.com for a Free plan, present a modal to the user that asks them to provide a credit card (likely on customers.gitlab.com).
• After the user account has a valid credit card associated with it, the user should be able to access their pool of free CI minutes.
• Purchasing additional CI minutes thereafter should be a 1-click operation.