Gallery example for modeling fixed-tilt arrays with pvfactors

[kandersolar]

• [ ] Closes #xxxx
• I am familiar with the contributing guidelines
• [ ] Tests added
• [ ] Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels and Milestone are assigned to the Pull Request and linked Issue.

Motivated by two interactions on the google group where the role of the axis_azimuth input for the pvfactors model was not clear when modeling fixed-tilt arrays:

• https://groups.google.com/g/pvlib-python/c/rPFn9G94Qf4/m/a1PQX5QPAgAJ
• https://groups.google.com/g/pvlib-python/c/0MFG0J59Xnc/m/ZqZyWmeJCQAJ

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Rendered example here: https://pvlib-python--1470.org.readthedocs.build/en/1470/gallery/bifacial/plot_pvfactors_fixed_tilt.html