Hide runner token in CI/CD settings page

What does this MR do?

EE MR, https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3773

• Hide runner token in CI/CD settings page
• Generalize secret value pattern

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Runner token is in plain-text when you visit the page and could be exposed.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #38019 (closed)