refactor(bootstrap,configuration,environment): add defaults/main.yml and extract hardcoded values

roles/configuration/defaults/main.yml

@@ -0,0 +1,7 @@
+---
+# Network configuration dispatch — maps OS name to the task file
+# that writes network config. Default (NetworkManager) applies to
+# all OSes not explicitly listed.
+configuration_network_task_map:
+  alpine: network_alpine.yml
+  void: network_void.yml