refactor(schema): move filesystem into system dictionary

roles/global_defaults/tasks/validation.yml

@@ -10,8 +10,8 @@
       - hypervisor_cfg is mapping
       - hypervisor_type is defined
       - hypervisor_type in ["libvirt", "proxmox", "vmware", "xen", "none"]
-      - filesystem is defined
-      - filesystem in ["btrfs", "ext4", "xfs"]
+      - system_cfg.filesystem is defined
+      - system_cfg.filesystem in ["btrfs", "ext4", "xfs"]
       - install_drive is defined
       - install_drive | string | length > 0
       - hostname is defined
@@ -272,7 +272,7 @@
       - (system_cfg.disks[0].size | float) > 0
       - (system_cfg.disks[0].size | float) >= 20
       - >-
-        filesystem != "btrfs"
+        system_cfg.filesystem != "btrfs"
         or (
           (system_cfg.disks[0].size | float)
           >= (