Make UMAP's init default to random on visualize_topics for reproducible visualization

[makramab]

What does this PR do?

Fixes #2403

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[MaartenGr]

Thank you for the PR!

At the moment, I'm very hesistant to add another parameter to the BERTopic class. I'd like to keep it all as small as possible with modularity as an important driver. As such, I would prefer to prevent model-specific parameters. Instead, I would suggest setting the init in visualize_topics to "random" as that should be the only (one of the few?) place(s) where it is used.

[makramab]

Thanks for the feedback! That makes sense. I’ll go ahead and change the visualize_topics function to set init="random" instead of adding a parameter.

[makramab]

Just pushed the changes, @MaartenGr. thanks again for the review!

[MaartenGr]

Wow, look at me waiting 3 weeks before answering... Sorry! Thank you for the changes and your patience. Looks good to me and can be merged.