feat: allow to modify /etc/hosts for testing

modules/nixos/base/networking.nix

@@ -18,4 +18,8 @@
     "ntp.aliyun.com" # Aliyun NTP Server
     "ntp.tencent.com" # Tencent NTP Server
   ];
+
+  # dynamically update /etc/hosts for testing
+  # Note that changes made in this way will be discarded when switching configurations.
+  environment.etc.hosts.mode = "0644";
 }