Enforce behaviour of limiting the max number of plots in a figure #354
Description
We still have the plot.max_subplots rcParam in arviz-base but we are not using it in arviz-plots. I think it should be possible to handle this at the PlotCollection and PlotMatrix level but it might need some extra care. Say we generate a truncated plot grid, the .viz attribute will miss variables/coordinates but plots may still ask to plot on that target which should then be handled gracefully.
Alternatively we could decide to remove that behaviour or keep things as simple as possible (simplest implementation that comes to mind is error out before calling create_plotting_grid if the number of plots in the figure is too high)