Add Tailscale keys to gitleaks

What does this MR do?

This MR adds Tailscale keys to the list of identifiable secret patterns. It includes Tailscale Auth keys, API keys, OAuth clients, Webhook keys, and SCIM keys.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests updated/added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer