title: Add button in fullcalendar v4 event
body: <p>In my fullcalendar v4.3.1 app I want to add some buttons with jsvascript function to events
  example with decision I make it as :</p>
  
  <pre><code>window.calendarEventsObject = new FullCalendar.Calendar(calendarEl, {
      plugins: ['dayGrid'],
  
      eventRender: function (eventInfo) {
  
          eventInfo.el.querySelector('.fc-title').append("&lt;i class='fa fa-external-link pull-right'&gt;7890&lt;/i&gt;");
          // I see text in title , but not html element, as I expected  
  
  
          // eventInfo.el.querySelector('.fc-title').html("&lt;i class='fa fa-external-link pull-right'&gt;7890&lt;/i&gt;");
          // If to uncomment  the lline above I got error eventInfo.el.querySelector(...).html is not a function
      },
  
      events: eventsList,
  
      showNonCurrentDates: false,
  
      editable: true,
      allDaySlot: true,
      selectable: true,
      selectHelper: true,
      selectOverlap: false,
      fixedWeekCount: false,
  
      aspectRatio: 0.4,
      height: 700,
  
  });
  </code></pre>
  
  <p>Which way is valid ?</p>
  
  <p>Thanks!</p>