Draw horizontal ray/line/grid

I want to draw a so called 'horizontal ray' or 'horizontal line' for some y points. I cannot find any option to do so for my charts. I tried using markers or even data labels but they are irrelevant. I'm currently using syncfusion library for drawing charts. Here is the image:

Image:

How can I achieve this?

this is the code I'm currently using, cartesian charts:

import 'dart:math';
import 'package:flutter/material.dart';
import 'package:syncfusion_flutter_charts/charts.dart';

class ChartAl extends StatefulWidget {
  @override
  _ChartPageState createState() => _ChartPageState();
}

late List<ChartData> chartData;

class _ChartPageState extends State<ChartAl> {
  late SelectionBehavior _selectionBehavior;

  @override
  void initState() {
    _selectionBehavior = SelectionBehavior(
        // Enables the selection
        enable: true);
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    chartData = getData();

    return Container(
      child: SfCartesianChart(
        primaryYAxis: NumericAxis(),
        primaryXAxis: DateTimeAxis(
            intervalType: DateTimeIntervalType.days,
            visibleMinimum: chartData[chartData.length - 29].x,
            visibleMaximum: chartData[chartData.length - 1].x),
        zoomPanBehavior: ZoomPanBehavior(
          enablePanning: true,
        ),
        series: <CartesianSeries<ChartData, DateTime>>[
          LineSeries(
            initialSelectedDataIndexes: <int>[2],
            selectionBehavior: SelectionBehavior(
              enable: true,
            ),
            // markerSettings: MarkerSettings(
            //   isVisible: true,
            //   shape: DataMarkerType.horizontalLine
            // ),
            // dataLabelSettings: DataLabelSettings(
            //     // Renders the data label
            //     isVisible: true),
            dataSource: chartData,
            xValueMapper: (ChartData tendencias, _) => tendencias.x,
            yValueMapper: (ChartData tendencias, _) => tendencias.y,
          )
        ],
        annotations: <CartesianChartAnnotation>[
          CartesianChartAnnotation(
            widget: Container(
              height: 1.0,
              width: 200,
              color: Colors.black,
            ),
            coordinateUnit: CoordinateUnit.point,
            x: DateTime(2018, 1, 10),
            y: 20,
            horizontalAlignment: ChartAlignment.near,
          )
        ],
        trackballBehavior: TrackballBehavior(
            enable: true,
            lineType: TrackballLineType.horizontal,
            tooltipSettings:
                InteractiveTooltip(enable: true, color: Colors.red)),
      ),
    );
  }
}

dynamic getData() {
  List<ChartData> data = [];
  for (int i = 1; i < 35; i++) {
    data.add(ChartData(DateTime(2018, 1, i), getRandomInt(10, 100).toInt()));
  }
  return data;
}

num getRandomInt(num min, num max) {
  final Random random = Random();
  return min + random.nextInt((max - min).toInt());
}

class ChartData {
  ChartData(this.x, this.y);
  final DateTime x;
  final int y;
}

I tried to draw it with a container with some width but as you see it does not work.