refactor(bootstrap): nest network fields under system.network to match main project schema

roles/global_defaults/defaults/main.yml

@@ -27,14 +27,15 @@ system_defaults:
   cpus: 0
   memory: 0 # MiB
   balloon: 0 # MiB
-  network: ""
-  vlan: ""
-  ip: ""
-  prefix: ""
-  gateway: ""
-  dns:
-    servers: []
-    search: []
+  network:
+    bridge: ""
+    vlan: ""
+    ip: ""
+    prefix: ""
+    gateway: ""
+    dns:
+      servers: []
+      search: []
   path: ""
   packages: []
   disks: []