Website: update billing info form for Fleet Sandbox users purchasing a license

[eashaw]

Closes: https://github.com/fleetdm/confidential/issues/1698 Changes:

• Added three inputs to the billing information form on /customers/new-license for organization, firstName and lastName
  • These inputs are only visible to Users who signed up on try-fleet/register (The Fleet sandbox registration page)
• Updated save-billing-info-and-subscribe.js to accept the three optional inputs and:
  • Update the user record with those values
  • Generate a license using the organization provided
  • Send an order confirmation email using the provided first and last names
• Updated the new-license page script to show the new inputs if the user's first and last name is set to be part of their email address
• Updated the input labels on the new-license page to match wireframes (`font-weight: 400)

[mike-j-thomas]

Thanks. @eashaw. Let's go over this together tomorrow to review the UI changes because I don't think I'm set up to view the new fields locally – I get a client-side error when I hit "Continue" to the billing details.

[eashaw]

@mikermcneil This PR has been updated with the User model changes.

[mikermcneil]

@eashaw Is this ready to merge?

[eashaw]

@mikermcneil I need to add the signupReason column and migrate the existing user data. I will put the site in maintenance mode and migrate the data before I merge this Pull request this today. I'll make an announcement in Slack before it happens.