nixos/grafana: create directory for notifiers provisioning

  notifierFile = pkgs.writeText "notifier.yaml" (builtins.toJSON notifierConfiguration);

  provisionConfDir =  pkgs.runCommand "grafana-provisioning" { } ''

    mkdir -p $out/{datasources,dashboards}

    mkdir -p $out/{datasources,dashboards,notifiers}

    ln -sf ${datasourceFile} $out/datasources/datasource.yaml

    ln -sf ${dashboardFile} $out/dashboards/dashboard.yaml

    ln -sf ${notifierFile} $out/notifiers/notifier.yaml