Add optional datamapplot visualization

[lmcinnes]

A basic version of using DataMapPlot for visualization. Documentation is just the API as I wasn't sure quite what you might want or need in the "getting started" docs for such a thing. Let me know if you have any requests or suggestions.

[MaartenGr]

Thank you for not only for this PR but also your work on UMAP, HDBSCAN, and This Not That! Truly wonderful and an amazing package for sharing annotated 2-dimensional embeddings.

With respect to the additional documentation in the examples, I think this deserves a spot but I am not sure where. Perhaps the quickstart here: https://maartengr.github.io/BERTopic/getting_started/quickstart/quickstart.html

But I can also add that later.

Lastly, at some point this should be integrated when saving a BERTopic model to the Hugging Face Hub. Having these images added to a readme would be great but it might take some effort to add that. I can check out what is necessary after this PR.

[MaartenGr]

Amazing, thanks for the hard work, both on the DataMapPlot package as well as this PR. It is merged! In the upcoming weeks, I plan to add it to the official documentation (https://maartengr.github.io/BERTopic/index.html) but I'll have to check the best location for it so it does not get buried in the docs.