Proposal to include `numberOfInstances` and `numberOfFeatures` qualities in the dataset description

The dataset description.xml contains some of the most useful meta-data of the dataset. I think the number of instances/rows and the number of features should be added here. Those features generally tend to be of the most interest (e.g. making a natural inclusion in openml-python's dataset representation), but requires an additional download which incurs user wait time and strains the server. There's already a precedent for including including features that directly reference the data (e.g. default_target_attribute, ignore_attribute and row_id_attribute), at the same time I realize we want to be careful about slowly creating one monolithic file. The specific use case that lead me to consider this is that the automl benchmark downloads qualities only to obtain the dataset dimensions. What do you think?

Start by reviewing dataset description.xml and the linked openml-python dataset representation, then trace how the automl benchmark downloads qualities to obtain dataset dimensions. Done means deciding the metadata placement and adding numberOfInstances and numberOfFeatures so consumers can obtain dimensions without the additional download.