Fix #78: Cannot specify target container when adding disks to a virtual machine resource

[PacoDw]

The storage_conntainer was added as a new attribute into the disk_list to reference a container in a VM.

Added:

• The attribute was added to the client to be part of the request to create the corresponding configuration.
• It also was added to the resource and data source.
• Test cases were created for resource and data source to validate it.
• Documentation for resource and data source was added.

Example Usage

data "nutanix_clusters" "clusters" {}

resource "nutanix_virtual_machine" "vm" {
  name                 = "myVm"
  cluster_uuid         = data.nutanix_clusters.clusters.entities.0.metadata.uuid
  num_vcpus_per_socket = 1
  num_sockets          = 1
  memory_size_mib      = 186

  disk_list {
    disk_size_bytes = 68157440
    disk_size_mib   = 65

    storage_config {
      storage_container_reference {
        kind = "storage_container"
        uuid = "2bbe67bc-fd14-4637-8de1-6379257f4219"
      }
    }
  }
}

closes #78