Resolve "Update the .com Registration Page to be GDPR Compliant"

What does this MR do?

Requires opt-in for terms of use and privacy policy to create an account on GitLab.com

Screenshots

Register form (only on GitLab.com)

Error state

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• 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 Backend maintainer
• EE specific content should be in the top level /ee folder
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #6262 (closed)