DOC: add plotting backends in visualization.rst
- [x] closes #30984 

@jorisvandenbossche  > There is just one thing I don't see clear. I think we may be adding content for two different audiences here. I think in the visualization user guide it makes sense to explain that other plotting backends exist, and how to use them. But I think the last part is not for pandas users, but for developers of pandas extensions. I think this should be in the Development documentation. 

Yes, what this PR is adding is meant for users, the development part already exists: https://dev.pandas.io/docs/development/extending.html#plotting-backends. See also my first review comment to remove this part here in the PR (and replace it with a link, what you said :-)) Saw the other comments but missed that one. Agree with all points. :)  Can you review this PR, please? thanks, @jorisvandenbossche for those corrections. The linting is clear now. does it require any change now? Thanks!