Add back copy for existing gcp accounts within offer banner

What does this MR do?

Follow up to gitlab-com/www-gitlab-com!12605 (merged), which adds copy for existing gcp accounts to about.gitlab.com

This MR adds the same copy within the UI

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?