Add an option to include the sum of the values of the datasets in the data labels

Currently it's possible to create stacked bars, but it's not possible to configure the datalabels to display the total values at the end of the stacks rather than the values on each fragment of the stack.
The problem is described (and solved) in this issue https://github.com/chartjs/chartjs-plugin-datalabels/issues/16 .

This feature would be about allowing to configure that for a chart created from a table in XWiki.