Doc fix: proxmox_cloud_init_disk

[maksimsamt]

Fix cdrom part

• cd => cdrom
• extra variable ${local.iso_storage_pool} fails and updates causes this issue:

iso = "cephfs:iso/tf-ci-***.iso" -> "cephfs:cephfs:iso/tf-ci-***.iso"

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  ~ update in-place

Terraform will perform the following actions:

  # proxmox_vm_qemu.cloud_vm_from_packer_template will be updated in-place
  ~ resource "proxmox_vm_qemu" "cloud_vm_from_packer_template" {
        id                     = "***/qemu/***"
        name                   = "***"
        tags                   = "***"
        # (67 unchanged attributes hidden)

      ~ disks {
          ~ scsi {
              ~ scsi11 {
                  ~ cdrom {
                      ~ iso         = "cephfs:iso/tf-ci-***.iso" -> "cephfs:cephfs:iso/tf-ci-***.iso"
                        # (1 unchanged attribute hidden)
                    }
                }

                # (1 unchanged block hidden)
            }
        }

        # (3 unchanged blocks hidden)
    }

Plan: 0 to add, 1 to change, 0 to destroy.