Additional labeling in visualize_documents

Nobody has claimed this yet.

I am doing some EDA on a corpus and was wondering if it was possible to make another layer of labeling for the individual documents. When you call ```visualize_documents``` the dots are plotted and color coded based on their respective topic, i was wondering if there was a way I could potentially alter the shape of the of the dot based on a factor, say for example I have a list of authors. I'd love to just use the BERTopic plotting mainly because I'm lazy 😅, but if its not possible at the moment I can recreate my own plots.

Start at the visualize_documents entry point and trace how document points are plotted and color-coded by topic. Check whether the plotting interface already accepts document-level metadata, then determine how an author or other factor could select marker shapes. Done means callers can provide such a factor and the resulting visualization uses distinct shapes while preserving topic colors.

Written by the indexing model from the issue text.