CAP*: expose kube-scheduler KUBE_MAX_PD_VOLS environment variable

[LolloneS]

There are cases in which we saw kube-scheduler fail to compute the maximum number of EBS volumes attachable to an instance. This is possibly due to volumes we currently attach to VMs "outside of Kubernetes". Basically, kube-scheduler knows that an EC2 instance has X slots for EBS volumes, but indeed only X-n are available. This leads to pods hanging while waiting for a volume to be attached.

The environment variable KUBE_MAX_PD_VOLS allows for telling kube-scheduler the maximum number of volumes attachable to each node in a cluster. As of now, we are setting it in Vintage via the k8s-initiator-app. It is currently only used on AWS, but would probably be helpful to expose such env variable (among others, I guess) in all providers.

As part of the migration to CAPI-native functionalities from the k8s-initiator App, we need this capability. I am assigning Phoenix and Turtles for visibility but if we want to make it available on all providers, then I assume it's Turtles.

[T-Kukawka]

hey @giantswarm/team-turtles, this seems more like a generic function to be implemented cross-providers