513 Deprecating Legacy Plot API

[bryannho]

Describe your changes

• Added deprecation warnings for legacy plot functions: .pie(), .bar(), and .plot()
• Added tests for deprecation warning messages
• Merged from master instead of individual branch

Issue number

Closes #513

Checklist before requesting a review

• Performed a self-review of my code
• Formatted my code with pkgmt format
• Added tests (when necessary).
• Added docstring documentation and update the changelog (when needed)

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📚 Documentation preview 📚: https://jupysql--870.org.readthedocs.build/en/870/

[edublancas]

please ensure tests are passing before requesting a review

[bryannho]

I was able to identify and fix the matplotlib bug. The tests I wrote in test_resultset.py were interfering with those in test_util.py. After re-writing my tests all checks are passed.

[edublancas]

@bryannho no need to respond to the PR comments when you begin working on stuff. it's fine if you respond to them after you finished the changes

[edublancas]

please review our contribution guidelines: https://ploomber-contributing.readthedocs.io/en/latest/contributing/responding-pr-review.html

when responding to PR comments, you need to add a link to the specific changes, so the reviewer can quickly spot them. add the corresponding links and request a review again