Add Clustering Extension for dendrogram

[kescobo]

Description

Extends #2755 to add a package extension for the Clustering.jl HClust type. Draft still because I wasn't sure how (or if I should) add the useheight parameter to enable usage of the heights in the HClust.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• Added an entry in CHANGELOG.md (for new features and breaking changes)
• Added or changed relevant sections in the documentation
• Added unit tests for new algorithms, conversion methods, etc.
• Added reference image tests for new plotting functions, recipes, visual options, etc.

[jkrumbiegel]

Weak deps are still dependencies as far as dependency hell, update churn etc. are concerned. So I'm generally hesitant to add more to Makie. Would this fit as an extension to Clustering instead?

[kescobo]

Fair enough - I'd be happy to ask over there. I saw the one extension here so thought it might be worth it, but Makie def. has more deps than Clustering.

That said, Clustering.jl hasn't had a commit merged in over a year, so not sure it's actively maintained.

[kescobo]

It could also be an option to just highlight the hcl_nodes function in the docs, not export it, and let people know how it works. It's not so complicated 🤷

[kescobo]

Well - that issue on Clustering.jl has not received any reply. Shall I just add this to the docs as an example?