feat(vm): enable qemu-guest-agent and set stop_on_destroy

- Add `qemu-guest-agent` enable/start command to `user-data.yml.tftpl` to ensure the agent is active immediately after provisioning.
- Set `stop_on_destroy = true` in the Proxmox VM resource definition to ensure graceful shutdown during Terraform destroy operations.

terraform/prod/01-virtual-machines.tf

@@ -24,10 +24,11 @@ locals {
 resource "proxmox_virtual_environment_vm" "vms" {
   for_each = var.virtual_machines
 
-  name      = "${each.key}.${var.domain_suffix}"
-  node_name = var.target_node
-  tags      = concat(["terraform-managed", "vm"], each.value.tags)
-  on_boot   = lookup(each.value, "on_boot", true)
+  name            = "${each.key}.${var.domain_suffix}"
+  node_name       = var.target_node
+  tags            = concat(["terraform-managed", "vm"], each.value.tags)
+  on_boot         = lookup(each.value, "on_boot", true)
+  stop_on_destroy = true
 
   # Configuration de l'agent QEMU
   agent {