allow to specify min_group_size in graphs that include grouping (e.g. using 'color', 'facet_row/col' etc.)

[Gilad-Dym]

when using 'grouped' plots, we'd often like to see trends/differentations between separate groups. however, it is common that some of the groups are very 'small', thus the data shown for them is confusing (and sometunes also distorts the rest of the plot, because the range can be very large).

i think allowing specification of min_group_size (Optional[int]) can be very beneficial, mitigating this issue, and eliminating the need of boilerplate code from the user side.

thank you for all your great work!