fix: skip clone storage override for linked Proxmox clones

The bpg/proxmox provider rejects clone.datastore_id when creating linked
clones. Only pass the target datastore when full clones are enabled so the
linked-clone baseline can provision from template 9000 successfully.

terraform/servers.tf

@@ -55,7 +55,7 @@ resource "proxmox_virtual_environment_vm" "nodes" {
 
   clone {
     vm_id        = var.proxmox_template_vm_id
-    datastore_id = var.proxmox_vm_storage_pool
+    datastore_id = var.proxmox_clone_full ? var.proxmox_vm_storage_pool : null
     full         = var.proxmox_clone_full
     retries      = 3
   }