schedulerName in kube_pod_* metrics group

[PigNatovsky]

What would you like to be added:
It would be great if we will have schedulerName in exported kube_info_metrics.
Why is this needed:
When we have more than one scheduler in the cluster, we need to aggregate some data by scheduler.
Describe the solution you'd like
It could be a metric called kube_pod_scheduler_name with labels set {pod, namespace, uid, schedulerName (or just name)}. Value can be taken from .spec.schedulerName.

[dashpole]

/assign @dgrisonnet
/triage accepted