[BUG] Modifying a VM resource always fails if name (an argument marked optional) is omitted or does not look like a "DNS name"

[fabacab]

This is basically the same issue as that described in #41 except instead of pool_id, the resource cannot be modified without a name argument (which is also marked as optional in this provider's documentation).

Here's the error:

Error: Received an HTTP 400 response - Reason: Parameter verification failed. (name: invalid format - value does not look like a valid DNS name)

To Reproduce

1. Set up a single-node Proxmox VE cluster (6.2-11 is what I'm using, the current stable release).
2. Create a simple, test VM with the following Terraform version 0.13.2 configuration (provider block is omitted for brevity):

   data "proxmox_virtual_environment_nodes" "pve_nodes" {}
   
   resource "proxmox_virtual_environment_file" "ubuntu_cloud_image" {
     content_type = "iso"
     datastore_id = "local"
     node_name    = data.proxmox_virtual_environment_nodes.pve_nodes.names[0]
   
     source_file {
       path = "https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-amd64.img"
     }
   }
   
   resource "proxmox_virtual_environment_vm" "testvm" {
     # Note that the `name` argument is commented out during VM creation.
     #name      = "must-be-here-to-modify-the-vm"
     node_name  = data.proxmox_virtual_environment_nodes.pve_nodes.names[0]
   
     disk {
       datastore_id = "local-lvm"
       file_id      = proxmox_virtual_environment_file.ubuntu_cloud_image.id
     }
   }

3. Apply the Terraform configuration with terraform apply; it should succeed.
4. However, now edit the Terraform config to make any non-destructive change such as adding (or removing) a network_device block without uncommenting the ostensibly optional name argument.
5. Run terraform apply again, and observe the error cited above.

Expected behavior

1. The documentation correctly describes the name value as a required argument, because it currently is. Or, preferably,
2. the provider does not allow creating a VM resource without a name argument for a proxmox_virtual_environment_vm since this situation will always result in a resource that can never be edited, only destroyed, once created.

[danitso-dp]

@fabacab do you still experience this issue with the latest version?