R1:67b7181f5226

Facts: Always render YYYY-MM-DD dates with eight digits in chart tooltips

Summary:
Always render dates in tooltips when hovering over data points in Burndown charts etc of the Facts application as `YYYY-MM-DD` instead of `YYYY-M-D` by converting the integer to a string and if its length is only one character, prepend a zero.

Closes T15819

Test Plan:
* Enable the Facts application, go to the Reports of a Project with task changes over time, hover over data points and read the tooltip.
* Check Console of…