shorter, cloud.gov-ier DNS names for NLBs

[bengerman13]

In order to remove implementation details from user-facing routes, we want TCP load balancers to have shorter names that do not reference cloud.gov and are not based on indices/counters

Acceptance Criteria

• GIVEN TCP routing is enabled in an environment
  AND multiple TCP domains exist in the environment
  WHEN I look for TCP domains
  THEN each domain should be a subdomain of cloud.gov
  AND no domain should reference Amazon/AWS
  AND it should be unclear what order domains were created in

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Security considerations

None

Implementation sketch

it probably makes sense to do something like ${digits}.tcp.${env}.cloud.gov, where digits is the first several digits from the NLB dns name from AWS and env is an environment identifier.

we should be able to do this with A/AAAA records, since I believe NLBs always have static IPs