Add support for units of measurement on BarChart component

[calippo]

The BarChart component doesn't expose props to set units of measurement of X and Y axes.

Our specific use case is a frequency (percentage) histogram:

We have percentage on Y axis and age buckets on X axis. Wrt to the screenshot, I would ignore the cumulative frequency in the legend unless this is offered by the library (It doesn't seem to be a standard feature).
I believe unit of measurement should be also reported in the tooltip (but I'm unsure what's standard behavior with recharts, this might not be a mandatory feature).
The frequency histogram is a specific use case in which the X axis unit can be omitted: "Age" in the title seems clear enough. However, I suppose setting X axis unit will be useful in general.