fix: include hashedLink in BOOKING_REQUESTED webhook payload

The CalendarEventBuilder.fromBooking() method was not calling
withHashedLink(), so hashedLink was always null in webhook payloads
built from stored bookings (including BOOKING_REQUESTED).

Changes:
- Add hashedLink relation to selectStatementToGetBookingForCalEventBuilder
  so the event type's hashed link is fetched from DB
- Call withHashedLink() in CalendarEventBuilder.fromBooking() to populate
  the field on the CalendarEvent
- Add tests verifying hashedLink is present/null in BOOKING_REQUESTED
  webhook payload

Co-Authored-By: morgan@cal.com <morgan@cal.com>