Add Filter by Check-In User for Event Attendees

It'll be beneficial to have the ability to filter attendees by the user who performed the check-in (i.e., the staff member or check-in user who validated each QR code). This is critical for events with multiple users managing the same check-in process, particularly when tracking redemptions by location, auditing internally, or reporting across different branches. Having this filter will improve accountability and streamline post-event reporting.