services.*ntp*: Add time-sync.target to ntp clients (#15714)

See: https://www.freedesktop.org/software/systemd/man/systemd.special.html#time-sync.target

nixos/modules/services/networking/chrony.nix

···
 
   ###### implementation
 
-  config = mkIf config.services.chrony.enable {
+  config = mkIf cfg.enable {
 
     # Make chronyc available in the system path
     environment.systemPackages = [ pkgs.chrony ];
···
         home = stateDir;
       };
 
-    systemd.services.ntpd.enable = false;
+    systemd.services.ntpd.enable = mkForce false;
 
     systemd.services.chronyd =
       { description = "chrony NTP daemon";
 
         wantedBy = [ "multi-user.target" ];
+        wants = [ "time-sync.target" ];
+        before = [ "time-sync.target" ];
         after = [ "network.target" ];
         conflicts = [ "ntpd.service" "systemd-timesyncd.service" ];
 

nixos/modules/services/networking/ntpd.nix

···
       { description = "NTP Daemon";
 
         wantedBy = [ "multi-user.target" ];
+        wants = [ "time-sync.target" ];
+        before = [ "time-sync.target" ];
 
         preStart =
           ''

nixos/modules/services/networking/openntpd.nix

···
     systemd.services.openntpd = {
       description = "OpenNTP Server";
       wantedBy = [ "multi-user.target" ];
-      wants = [ "network-online.target" ];
+      wants = [ "network-online.target" "time-sync.target" ];
+      before = [ "time-sync.target" ];
       after = [ "dnsmasq.service" "bind.service" "network-online.target" ];
       serviceConfig.ExecStart = "${package}/sbin/ntpd -d -f ${cfgFile} ${cfg.extraOptions}";
     };