adding model evaluation plots to improve the examples

[edublancas]

Description

Hi mxnet team!

I noticed the examples do not contain model evaluation plots; adding them would be great so beginners can visualize their model's performance. I'm the maintainer of a package for ML model visualization, I'm happy to open a PR editing some of the examples! Let me know what you think!

References

• Github repo

[github-actions]

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