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.
Split up unused key validation in config entry decode for oss/ent.
This is needed so that we can return an informative error in OSS if namespaces are provided.
