feat(prod): add monitoring VM configuration to tfvars

Populate the previously empty `virtual_machines` map in the production environment. This defines a new "monitoring" VM instance running Debian with 2 cores, 4GB RAM, and 30GB disk space, assigned to IP 192.168.1.161.

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 = {
+    "monitoring" = {
+        os       = "debian"
+        cores    = 2
+        memory   = 4096
+        disk_gb  = 30
+        ip       = "192.168.1.161"
+        gateway  = "192.168.1.254"
+        tags     = ["monitoring"]
+    }
+}
 
 #############################
 # Notes de configuration