Switch database load balancing over to SVC records
Related to https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/7656
In https://gitlab.com/gitlab-org/gitlab-ee/issues/13732 we added support for SVC records in database load balancer lookups.
We should migrate omnibus over to using these records by default. This will give us greater flexibility in future with further changes, such as additional additional pgbouncer hosts per postgres host.