Add unit to axis labels

[sophiamersmann]

Core problem

It would help understanding the chart if we added the unit to axis labels.

Proposed solution

Add the unit in parens, like 'Axis label (unit)'. It might be redundant in some cases, but overall an improvement, I think. Tooltips show the unit in parens, so we could use the same logic for axis labels.

Screenshots

Two examples where the unit would be useful

One example where an author has changed the axis label to clarify the unit

One example where no unit would be added