[Feature] - Allow autoscale the node quantity in `vultr_kubernetes_node_pools`

[fhisamoto]

The vultr api allows create or update k8s node pools with desired quantity within (min_nodes, max_nodes) range. Would be awesome if I could do the same with terraform. So the vultr_kubernetes_node_pools could be written

resource "vultr_kubernetes_node_pools" "workers-nodepool" {
  cluster_id    = vultr_kubernetes.k8.id
  auto_scaler   = true
  node_quantity = 2
  min_nodes     = 1
  max_nodes     = 4
  plan          = "vc2-1c-2gb"
  label         = "worker"
  tag           = "worker"
}

and vultr_kubernetes would be

resource "vultr_kubernetes" "k8" {
  region  = var.region
  label   = "vke-cluster"
  version = "v1.23.5+2"

  node_pools {
    auto_scaler   = true
    node_quantity = 2
    min_nodes     = 1
    max_nodes     = 4
    plan          = "vc2-1c-2gb"
    label         = "np-3"
  }
}

[ddymko]

@fhisamoto we'll look to get this added into the next TF release