Add cluster_columns to fastai.tabular

I’m currently learning fastai using fastbook, the course and working on some kaggle competitions and I found cluster_columns from fastbook to be a very useful function to quickly get some info about column correlation. I think it would be very helpful for me and others if this was added to fastai’s tabular submodule since it’s hard to find and there is not really any documentation for fastbook (at least when I looked it up)