The API is a copy of output/v1alpha1 with a minor difference
where output/v1alpha2.BootstrapToken embeds
bootstraptoken/v1.BootstrapToken instead of
kubeadm/v1beta2.BootstrapToken.
Embedding the later is an undesired binding between the "kubeadm"
and "output" groups, preventing the eventual deprecation and removal
of the kubeadm.v1beta2 API.
This new output API version, unlike v1alpha1, does not include
defaulting which is not needed.