Setup DNS for internal routing

[stevesloka]

Gimbal is focused on handling Ingress traffic. But another use-case is to handle internal application routing for multiple clusters.

A good example would be to have an application deployed to a cluster. If maintenance is required on that cluster, then spin up the application on a second and slowly transition work over to the new cluster. By providing a single DNS endpoint within the cluster, any consumer of the application doesn't need to change logic.

// cc @hhoover