Include reservation email in the export of the attendees data

**Is your feature request related to a problem? Please describe.**
The email of the reservation it's a super necessary data for checking which people is the responsible for which ticket.

**Describe the solution you'd like**
The email of the reservation should be included in the download/export of all the attendees data

**Describe alternatives you've considered**
There is no such alternative and crossing email reservations with tickets it's something super useful

**Additional context**
N/A