Fixed #21755 -- Added FK support for REQUIRED_FIELDS.

Can we use `raw_value = input(force_str('%s%s: ' % (capfirst(field.verbose_name), ' (%s.%s)' % ('FIXME', field.rel.field_name) if field.rel else '')))`  where FIXME is the FK model name (not it's verbose name) so the output is something like "Email (Email.email): "?