nsswitch: add systemd module

In order for DynamicUser = true to work in services, we need the
nss-systemd module to be able to resolve the user and group names
generated dynamically.

Changed files
+2 -1
nixos
modules
config
+2 -1
nixos/modules/config/nsswitch.nix
···
passwdArray = [ "files" ]
++ optional sssd "sss"
++ optionals ldap [ "ldap" ]
-
++ optionals mymachines [ "mymachines" ];
+
++ optionals mymachines [ "mymachines" ]
+
++ [ "systemd" ];
shadowArray = [ "files" ]
++ optional sssd "sss"