AWS HyperShift clusters' nodes cannot join cluster with custom domain name in DHCP Option Set

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1. Create a VPC for a HyperShift/ROSA HCP cluster in AWS
2. Replace the VPC's DHCP Option Set with another with a custom domain name (example.com or really any domain of your choice)
3. Attempt to install a HyperShift/ROSA HCP cluster with a nodepool

All EC2 instances will fail to become nodes. They will generate CSR's based on the default domain name - ec2.internal for us-east-1 or ${region}.compute.internal for other regions (e.g. us-east-2.compute.internal)

Either that they become nodes or that we document that custom domain names in DHCP Option Sets are not allowed with HyperShift at this time. There is currently no pressing need for this feature, though customers do use this in ROSA Classic/OCP successfully.

This is a known gap currently in cluster-api-provider-aws (CAPA) https://github.com/kubernetes-sigs/cluster-api-provider-aws/issues/1691