Update banner that appears on the Sign In Page

Summary

Update the banner that appears on the /sign_in page when a new user is redirected here when attempting to purchase Premium from about.gitlab.com.

Context

Idea came out of the discussion that occurred in this thread. We want to improve the UX of this banner to make it easier for users to continue with the Premium purchasing process.

Solution

🔗 Figma File

Update the banner that appears on the /sign_in page.

Current State	Updated State

Product Requirements

• Update Alert style from danger to info
• Update copy in the banner
• Reposition the main CTA to be in-line with the main copy
• Have the primary CTA be Register now which would link users to the /sign_up page
• /users/sign_up continues to operate as expected

Outstanding Questions

• Is it possible to use a banner design like the one proposed in this issue?
• What are the other paths that lead to this banner appearing on the /sign_in page

UX Checklist

• UX Review
• Growth Review
• TW Review (If Necessary)
• PMM Review (If Necessary)