Add Vars and VarsTemplate fields to the NodeFeatureGroup spec. This
enables construction of complex rule hierarchies by making it possible
to reference/use results of preceding rules when evaluating a rule.
The NodeFeatureGroup is an NFD-specific custom resource that is designed for
grouping nodes based on their features. NFD-Master watches for NodeFeatureGroup
objects in the cluster and updates the status of the NodeFeatureGroup object
with the list of nodes that match the feature group rules. The NodeFeatureGroup
rules follow the same syntax as the NodeFeatureRule rules.
Signed-off-by: Carlos Eduardo Arango Gutierrez <eduardoa@nvidia.com>