nixos/prometheus: use the non-alias path for dovecot exporter (#380619)

    serviceConfig = {

      DynamicUser = false;

      ExecStart = ''

        ${pkgs.prometheus-dovecot-exporter}/bin/dovecot_exporter \

        ${lib.getExe pkgs.dovecot_exporter} \

          --web.listen-address ${cfg.listenAddress}:${toString cfg.port} \

          --web.telemetry-path ${cfg.telemetryPath} \

          --dovecot.socket-path ${escapeShellArg cfg.socketPath} \