Implement base EventController endpoints

[TyostoKarry]

Implement controller endpoints to manage event creation, listing, and retrieval as described in the Eventshuffle API specification.

• Add endpoints:
  • GET /api/v1/event/list: list all events.
  • POST /api/v1/event: create a new event.
  • GET /api/v1/event/{id}: show details of one event.
• Create EventController under controller.
• Create DTOs for request and response payloads.
• Add EventService for business logic and EventRepository for persistence.
• Validate that name is not blank, and dates array is not empty and contains valid ISO 8601 date strings.