nixos/nats: Shut down gracefully, and prevent automatic restart on deliberate stop (#448023)

          Type = "simple";

          ExecStart = "${pkgs.nats-server}/bin/nats-server -c ${configFile}";

          ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";

          ExecStop = "${pkgs.coreutils}/bin/kill -SIGINT $MAINPID";

          KillMode = "mixed";

          KillSignal = "SIGUSR2";

          SuccessExitStatus = [

            0

            "SIGUSR2"

          ];

          TimeoutStopSec = "150"; # must exceed lame_duck_duration, which defaults to 2min

          Restart = "on-failure";

          User = cfg.user;