No config entry needs a Kind field. It is only used to determine the Go type to
target. As we introduce new config entries (like this one) we can remove the kind field
and have the GetKind method return the single supported value.
In this case (similar to proxy-defaults) the Name field is also unnecessary. We always
use the same value. So we can omit the name field entirely.
This config entry is being renamed primarily because in k8s the name
cluster could be confusing given that the config entry applies across
federated datacenters.
Additionally, this config entry will only apply to Consul as a service
mesh, so the more generic "cluster" name is not needed.
