Add kwarg to avoid alternate row shading with az.plot_forest

[u7576869]

Description

Adding a new parameter alternate_row_shading to give the user control over alternate row shading. Setting this to false will result in a more clear graph in many cases.

Checklist

• [ ] Follows official PR format
• [ ] Includes a sample plot to visually illustrate the changes (only for plot-related functions)
• [ ] New features are properly documented (with an example if appropriate)?
• [ ] Includes new or updated tests to cover the new feature
• [ ] Code style correct (follows pylint and black guidelines)
• [ ] Changes are listed in changelog

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:books: Documentation preview :books:: https://arviz--2286.org.readthedocs.build/en/2286/