NAT: Clarify what happens when user passes blank prefix lists, non-empty exclusion prefix lists #779
Description
We need to clarify the exact semantics of empty ips/as_range and non-empty nots/not_as.
We currently reject this configuration when validating VpcExpose objects. If it turns out this configuration is valid, we need to adjust validation (and NAT code) accordingly, as we initially tried to do in #662.