POC distributed DNS shared records

[maleck13]

What

We intend for our controllers to coordinate via the DNS zone. This sometimes mean they will need to set values shared by other clusters. It means also that for a short period the actual zone can fall out of sync.
Our design allows for this as the source of truth for each cluster is in the cluster itself, but we want to do a POC here to validate that the record set becomes consistent and does so relatively quickly. We also want to use Google DNS to re-familiarise ourselves with this provider as we sometimes succumb to AWS bias.
Finally we want to do this POC with the simple strategy to reduce the overhead and work while still retaining the core problem set
( sharing a record for updates and clean up)

[mikenairn]

POC branches:

DNS Operator: https://github.com/Kuadrant/dns-operator/tree/multicluster_external_dns
External DNS: https://github.com/Kuadrant/external-dns/tree/multicluster_external_dns_poc

PR to move to external-dns for single cluster(and eventually multi cluster): #43