Allow for clickable charts that query Drupal

[mjordan]

It would be useful to provide the ability to click on a segment in a pie chart, for example, and launch a browser tab that queries Drupal for all the pages counted in that segment (e.g. for a given taxonomy term). This is not a built-in feature of Chart.js but chartjs/Chart.js#4639 provides some sample JavaScript code that could be used for this.