nixos/alloy: automaticlly include all .alloy files in reload trigger (#388634)

        configuration file via `environment.etc."alloy/config.alloy"`.

        This allows config reload, contrary to specifying a store path.

        A `reloadTrigger` for `config.alloy` is configured.

        Other `*.alloy` files in the same directory (ignoring subdirs) are also

        honored, but it's necessary to manually extend

        `systemd.services.alloy.reloadTriggers` to enable config reload

        during nixos-rebuild switch.

        All `.alloy` files in the same directory (ignoring subdirs) are also

        honored and are added to `systemd.services.alloy.reloadTriggers` to

        enable config reload during nixos-rebuild switch.

        This can also point to another directory containing `*.alloy` files, or

        a single Alloy file in the Nix store (at the cost of reload).

  config = lib.mkIf cfg.enable {

    systemd.services.alloy = {

      wantedBy = [ "multi-user.target" ];

      reloadTriggers = [ config.environment.etc."alloy/config.alloy".source or null ];

      reloadTriggers = lib.mapAttrsToList (_: v: v.source or null) (

        lib.filterAttrs (n: _: lib.hasPrefix "alloy/" n && lib.hasSuffix ".alloy" n) config.environment.etc

      );

      serviceConfig = {

        Restart = "always";

        DynamicUser = true;