Add a text description to the analytics charts

Related to WCAG 2.1 level A criteria 1.1.1: non-text content
https://www.w3.org/TR/WCAG21/#non-text-content

Charts provided in the administration > analytics menu do not have a text counterpart describing the results.

To be fully compatible with this criteria, a dynamic description needs to be generated based on the current results, as described in the example below.

Examples
A data chart
A bar chart compares how many widgets were sold in June, July, and August. The short label says, "Figure one - Sales in June, July and August." The longer description identifies the type of chart, provides a high-level summary of the data, trends and implications comparable to those available from the chart. Where possible and practical, the actual data is provided in a table.