This introduces a polymorphic scale client capable of operating against
scale subresources which return different group-versions of Scale. The
scale subresources may be in group-versions different than the scale
itself, so that we no longer need a copy of every scalable resource in
the extensions API group.
To discovery which Scale group-versions go to which subresources,
discovery is used.
The scale client maintains its own internal versions and conversions to
several external versions, with a "hub" version that's a copy of the
autoscaling internal version.
It currently supports the following group-versions for Scale subresources:
- extensions/v1beta1.Scale
- autoscaling/v1.Scale
Kubernetes-commit: d61a2d90372c301dd11088df8941acf2bb01c38c
