Add Registration Deadline to Events

[PublisherName]

Description

Currently, events do not have a registration deadline field. Adding this feature will enable organizers to specify a cutoff date for participants to register, improving event management and planning.

Proposed Solution

1. Add a registration_deadline field to the Event model.
2. Implement logic to prevent new registrations after the deadline has passed.
   • Show a relevant error message if a user attempts to register after the deadline.