Added tracking to boards add issues

app/assets/javascripts/boards/index.js

@@ -332,6 +332,8 @@ export default () => {
             class="btn btn-success gl-ml-3"
             type="button"
             data-placement="bottom"
+            data-track-event="click_button"
+            data-track-label="board_add_issues"
             ref="addIssuesButton"
             :class="{ 'disabled': disabled }"
             :title="tooltipTitle"