Follow-up from "Frontend implementation for improved trial sign-up experience for GitLab.com (SaaS) users"

The following discussions from !16732 (merged) should be addressed:

• @mayra-cabrera started a discussion: (+5 comments)

  Would it be possible to reuse our built-in namespaces select instead of building it from scratch? You can see it in action on the "Transfer Project" section

  transfer_project_select

  The code for it is located on NamespacesHelper#namespaces_option