In most line graphs you find on the internet the marked datapoint will be marked both with a tooltip and with a vertical line, helping the user see which datapoint they have selected. For instance, consider this graph:
https://fred.stlouisfed.org/series/FPCPITOTLZGUSA
When you hover over a certain point, a thin grey vertical line appears showing which one it is. How can I get the same effect with chartjs?