feat(tooltip): prop to format values in tooltip was added

[ahtohbi4]

@plouc property to format values in tooltip was added for components Bar, Bubble, Chord, HeatMap, Line, Pie, Radar, Sankey and Stream.

[plouc]

@ahtohbi4, thank you for this nice addition!
Just 2 suggestions:

• It could be nice to have the same logic as other formatting related properties, supporting d3.format or custom function
• I tend to prefer flat properties (appart from specific configs such as axes) because it's easier to diff those, so in this case tooltipFormat

[ahtohbi4]

@plouc, everything was fixed.

[plouc]

@ahtohbi4, thank you, and you updated the stories 👍

[plouc]

I cannot release it for now, will try to do it next week.