Is your feature request related to a problem? Please describe.
Dealing with horizontal offset in horizontal bar charts can be challenging with different value label box sizes: a single offsetX size won't fits all possible values.
While for vertical placement it is possible to build a sensible positional heuristic based on the fontSize parameter, with the horizontal version it is more tricky as it's not known the maximum value at init time.

Describe the solution you'd like
It would be nice to have both offsetX and offsetY be of type function, so that the developer could return a dynamical value for each value label based on the valueBox to precisely position the label.

Stretch goal: it would be nice to have also an additional overrideChartMargins option, which automagically handles "outside" labels by overriding theme margins for the particular direction.

Describe alternatives you've considered
Another approach would be to provide a fixed outside behaviour as in #784 and let the develop build offset tweaks on top of it.
As for the additional overrideChartMargins option alternative, for horizontal chart, I think there's nothing I can think of for it.

Additional context
This feature would make it possible to provide the correct behaviour for a outside label positioning as shown in the GIF above.