feat(heatmap): allow label formatting

[robonyong]

Had a similar need to #1425, wanted to change the label that's shown in a heatmap cell.

I copied the way Bar handles a label prop for this one, please let me know if there's a different preferred way to do so now.

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[wyze]

First off, sorry for the late review!

We are trying to get rid of recompose so we'd like to avoid adding any new code containing that. That said we can take the recompose code you did and create a variable with useMemo hook!

const getLabel = useMemo(() => getLabelGenerator(label, labelFormat), [label, labelFormat])

[robonyong]

@wyze Makes sense! I removed the recompose stuff & switched to using useMemo inside the useHeatmap hook

[wyze]

Looks great, thanks!

Also, thanks for adding stories for the canvas implementation.