title: Can I place flags over y-axis HighCharts
body: <p>Hey I am using HighCharts as my main graph library. 
  I would like to highlight(or flag) specific points on y-axis.
  I know that I can have flags over x-axis, can I do it for the <strong>y-axis too</strong>?</p>
  
  <p>I am attach an example of flags over x-axis, can I implement this for the y-axis the same way?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>$(function () {
      $.getJSON('https://www.highcharts.com/samples/data/jsonp.php?filename=usdeur.json&amp;callback=?', function (data) {
  
          var lastDate = data[data.length - 1][0],  // Get year of last data point
              days = 24 * 36e5; // Milliseconds in a day
  
          // Create the chart
          $('#container').highcharts('StockChart', {
  
              rangeSelector: {
                  selected: 1
              },
  
              title: {
                  text: 'USD to EUR exchange rate'
              },
  
              yAxis: {
                  title: {
                      text: 'Exchange rate'
                  }
              },
  
              series: [{
                  name: 'USD to EUR',
                  data: data,
                  id: 'dataseries',
                  tooltip: {
                      valueDecimals: 4
                  }
              }, {
                  type: 'flags',
                  name: 'Flags on series',
                  data: [{
                      x: lastDate - 60 * days,
                      title: 'On series'
                  }, {
                      x: lastDate - 30 * days,
                      title: 'On series'
                  }],
                  onSeries: 'dataseries',
                  shape: 'squarepin'
              }, {
                  type: 'flags',
                  name: 'Flags on axis',
                  data: [{
                      x: lastDate - 45 * days,
                      title: 'On axis'
                  }, {
                      x: lastDate - 15 * days,
                      title: 'On axis'
                  }],
                  shape: 'squarepin'
              }]
          });
      });
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"&gt;&lt;/script&gt;
  &lt;script src="https://code.highcharts.com/stock/highstock.js"&gt;&lt;/script&gt;
  &lt;script src="https://code.highcharts.com/stock/modules/exporting.js"&gt;&lt;/script&gt;
  
  
  &lt;div id="container" style="height: 400px; min-width: 310px"&gt;&lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>