feat(prod): add IP Fabric virtual machine configuration

Update the production terraform variables to define the 'ipfabric'
virtual machine. This replaces the empty VM map with specific
resource allocations:

- Resources: 4 vCPUs, 16GB RAM, 128GB Storage
- Network: Static IP 192.168.1.161
- OS tag: ipfabric

This configuration enables the provisioning of the IP Fabric node in the
production environment.

terraform/prod/terraform.tfvars

@@ -33,7 +33,17 @@ admin_ssh_public_key_path = "~/.ssh/keys/id_rsa.pub"
 # Utilisateur par défaut sur les VMs
 default_vm_user = "damien"
 
-virtual_machines = {}
+virtual_machines = {
+  "ipfabric" = {
+    os      = "ipfabric"
+    cores   = 4
+    memory  = 16384
+    disk_gb = 128
+    ip      = "192.168.1.161"
+    gateway = "192.168.1.254"
+    tags    = ["ipfabric"]
+  }
+}
 
 #############################
 # Notes de configuration