Add Cloud-Init automation with Tailscale

The commit rephrases the README to focus on Cloud-Init setup and removes
unused Ansible code, making Tailscale configuration automatic.

Subject line: Replace Ansible with automated Cloud-Init configuration

Body: Refactors infrastructure bootstrapping to leverage Cloud-Init
instead of Ansible for initial VM setup, particularly with respect to
Tailscale installation and authentication.

This simplifies the architecture by: - Removing manual post-provisioning
Ansible steps - Automating Tailscale setup via Cloud-Init - Updating
documentation to reflect new workflow

terraform/prod/02-cloud-init.tf

@@ -0,0 +1,26 @@
+# Fichier: terraform/prod/02-cloud-init.tf
+
+resource "proxmox_virtual_environment_file" "cloud_config" {
+  for_each = var.virtual_machines
+
+  node_name    = var.target_node
+  datastore_id = "local"
+  content_type = "snippets"
+
+  source_raw {
+    data = templatefile("${path.module}/../../cloud-init/user-data.yml.tftpl", {
+      # Variables pour définir les informations de l'utilisateur
+      username = lookup(each.value, "username", var.default_vm_user)
+      ssh_key  = file(var.admin_ssh_public_key_path)
+
+      # Variables pour définir les informations de la VM
+      hostname = "${each.key}.${var.domain_suffix}"
+
+      # Nouvelles variables pour Tailscale
+      vm_name            = each.key # Le nom de la VM (ex: "web-01")
+      tailscale_auth_key = var.tailscale_auth_key
+    })
+
+    file_name = "${each.key}-cloud-init.yml"
+  }
+}