Document how to associate dns to ip for clusters
In the CI/CD > Kubernetes details page we can install an ingress controller for the cluster, and see the related external IP address there. But we still need to better explain how to use it in conjunction with a wildcard DNS.
We should improve documentation in https://docs.gitlab.com/ee/user/project/clusters/index.html#getting-the-external-ip-address to explain this additional step, with a similar approach we have in https://docs.gitlab.com/ee/topics/autodevops/quick_start_guide.html#point-dns-at-cluster-ip.