example-get-started: update plots to use dvclive

[dberenbaum]

Closes https://github.com/iterative/example-repos-dev/issues/234.

Updates two plots to use dvclive:

• precision recall (using log_sklearn_plot with additional kwarg drop_intermediate=True)
• feature importance (using log_image matplotlib support)

All the plots are now dvclive, which simplifies the code and dvc.yaml a bit. I ended up caching all of them, because I don't see much upside to keeping the tsv/json plots in git, and it simplifies dvc.yaml. We lose explaining how to make more custom plots, but I think that's outside the scope of get started. If we want more custom plots, we can try to think of more complex visualizations to include.

Todo for deployment:

• [x] Deploy the updated code
• [x] Deploy the updated repo (experiments, PRs, etc.; see readme)
• [x] Update Studio demo
• [ ] @shcheklein Do we need to update https://github.com/iterative/example-get-started-azure-private-fixture, https://github.com/iterative/example-get-started-http-private-fixture, and https://github.com/iterative/example-get-started-ssh-private-fixture?

[dberenbaum]

Merging but not deploying yet because I am working on some larger changes and don't think it's worth it for this change alone.