Support for subsetting by dimensions when plotting a multidimensional model

[timbo112711]

@TeemuSailynoja and I have ran into a case where the model has too many dimensions (for example - channel, geo, user type) and plotting things like contributions_over_time can either be not visible or throw a warning WARNING: Output too large, the following mime types were removed from the output: image/png (on Databricks).

We will need add arguments to the function(s) to support subsetting by dimensions, so that the plots can be easily read and rendered.

Places that this will be needed:

• in contributions_over_time
• in plot.budget_allocation