Add Check-in user information in the attendee export file

Adding a column in the attendee CSV export that shows the check-in user—the staff member who scanned the attendee's QR code. This detail is especially important for stores that operate across multiple physical locations or have merchant partners with several branches. Each location may have different check-in users managing QR code validations, and having visibility into who performed each check-in would allow us to generate more accurate reports for our merchant partners. It would also enable better tracking of ticket redemptions by location or by individual team member.