Disallow taints having a key with "kubernetes.io/" or "*.kubernetes.io/"
prefix. This is a precaution to protect the user from messing up with
the "official" well-known taints from Kubernetes itself. The only
exception is that the "nfd.node.kubernetes.io/" prefix is allowed.
However, there is one allowed NFD-specific namespace (and its
sub-namespaces) i.e. "feature.node.kubernetes.io" under the
kubernetes.io domain that can be used for NFD-managed taints.
Also disallow unprefixed taint keys. We don't add a default prefix to
unprefixed taints (like we do for labels) from NodeFeatureRules. This is
to prevent unpleasant surprises to users that need to manage matching
tolerations for their workloads.
