nixos/etc: keep directories in derivation name

This changes eg. etc-timesyncd.conf to etc-systemd-timesyncd.conf which
better reflects the actual location of the config file.

Changed files
+1 -1
nixos
modules
system
etc
+1 -1
nixos/modules/system/etc/etc.nix
···
config = {
target = mkDefault name;
source = mkIf (config.text != null) (
-
let name' = "etc-" + baseNameOf name;
+
let name' = "etc-" + lib.replaceStrings ["/"] ["-"] name;
in mkDerivedConfig options.text (pkgs.writeText name')
);
};