(proposal) Add external-dns to the Kubernetes cluster with an ingress (and a loadbalancer)

[dduportal]

While working on #2752 , we tried to delegate a DNS zone to DigitalOcean to support the new doks-public cluster.
The idea was to use terraform for the cluster, but also for its public external load-balancer and the associated DNS, without any requirements to Azure (where we centralize the DNS zone apex).

However as per jenkins-infra/digitalocean#81, DigitalOcean recommends to let Kubernetes managing the Load Balancer (and not defining it outside like with terraform).

Idea for later; using external-dns is theses cases:

• The Kubernetes controller will then be able to manage the LB, the DNS records and the certificates.
• Using delegated DNS zones per cloud would help by only allowing DNS record in a sub-domain (safety)

[dduportal]

Closing as this issue is not needed anymore: we do not use DigitalOcean Kubernetes today, and we have successfully delegated DNS to AWS from Azure