refactor(global_defaults): add idempotency guards to normalization tasks

roles/global_defaults/tasks/system.yml

@@ -1,9 +1,12 @@
 ---
-- name: Validate raw system input types
-  ansible.builtin.include_tasks: _validate_input.yml
+- name: Normalize system and disk configuration
+  when: system_cfg is not defined
+  block:
+    - name: Validate raw system input types
+      ansible.builtin.include_tasks: _validate_input.yml
 
-- name: Normalize system configuration
-  ansible.builtin.include_tasks: _normalize_system.yml
+    - name: Normalize system configuration
+      ansible.builtin.include_tasks: _normalize_system.yml
 
-- name: Normalize disk configuration
-  ansible.builtin.include_tasks: _normalize_disks.yml
+    - name: Normalize disk configuration
+      ansible.builtin.include_tasks: _normalize_disks.yml