Add nav entries for new Secure pages

Add navigation item to global navigation

• Link to the merge request that introduced the new page:
  • Docs: Split SAST Troubleshooting to separate page (gitlab!128513 - merged)
    • Target page: https://docs.gitlab.com/ee////user/application_security/sast/troubleshooting.html
  • Docs: Move 'generate test vulns' topic to dev docs (gitlab!127804 - merged)
    • Target page: https://docs.gitlab.com/ee/development/sec/generate_test_vulnerabilities.html
• Give the MR a descriptive title.
• Optional. Link to the review app showing the new page:
  • https://rd-add-nav-entries-for-secure.docs.gitlab-review.app/ee/user/application_security/sast/troubleshooting.html
  • https://rd-add-nav-entries-for-secure.docs.gitlab-review.app/ee/development/sec/generate_test_vulnerabilities.html