text: Title: api: Extend validity of domain renewal confirmation links
  Body: This only affects dynDNS domains.
  
  Currently, the validity is 24 hours. It should be at least a week, or until the scheduled domain deletion date.
  
  The validity period is not encoded in the link, but determined at validation time. At that point, the payload (including domain name) is not yet known, so using the scheduled domain deletion date is not an option.
  
  Alternatively, we may just set it to 4 weeks: We delete domains 4 weeks after the first notification, so that would cover all cases.
  
  No expiration would also work (links are invalidated anyway when the domain owner or other significant things change). ~However, that opens the opportunity for people to renew their domain infinitely without reading their emails. That's not what we want - if people want automation, they should renew their domain by changing some DNS information.~ `Domain.renewal_changed` is included in the action state, so using the link invalidates it as well.
  
  Implementation proposal: At validation time in `AuthenticatedActionSerializer`, use `self.context['view']` to retrieve the view, and make the validity period an attribute of the view classes (with a reasonable default in the base class).