More broken links (internal and external)

[echedey-ls]

Describe the bug
#2488 is my source of inspiration. Grep'ed for user_guide pages, and these ones are the broken ones. Also, I've run linkchecker (output below). Feel free to provide other useful inputs for grep to check for broken links.

Broken user_guide references

README.md:77:https://pvlib-python.readthedocs.io/en/stable/user_guide/installation.html

docs/sphinx/source/conf.py:163:https://pydata-sphinx-theme.rtfd.io/en/latest/user_guide/configuring.html

Linkchecker output

(        whatsnew: line   97) broken    https://github.com/solphie-pelland - 404 Client Error: Not Found for url: https://github.com/solphie-pelland
(        whatsnew: line  215) broken    https://github.com/thunderfish24 - 404 Client Error: Not Found for url: https://github.com/thunderfish24
(contributing/style_guide: line   31) broken    https://help.github.com/articles/about-pull-request-merges/#squash-and-merge-your-pull-request-commits - Anchor 'squash-and-merge-your-pull-request-commits' not found
(reference/generated/pvlib.iotools.get_pvgis_hourly: line    1) broken    https://re.jrc.ec.europa.eu/api/v5_2/ - 404 Client Error: NOT FOUND for url: https://re.jrc.ec.europa.eu/api/v5_2/
(reference/generated/pvlib.clearsky.bird: line   57) broken    https://www.nrel.gov/docs/legosti/old/761.pdf - 404 Client Error: Not Found for url: https://www.nrel.gov/docs/legosti/old/761.pdf       
(reference/generated/pvlib.spectrum.get_reference_spectra: line   27) broken    https://www.nrel.gov/grid/solar-resource/assets/data/astmg173.xls - 404 Client Error: Not Found for url: https://www.nrel.gov/grid/solar-resource/assets/data/astmg173.xls
(reference/generated/pvlib.spectrum.spectral_factor_jrc: line   54) broken    https://www.researchgate.net/publication/256080247 - 403 Client Error: Forbidden for url: https://www.researchgate.net/publication/256080247
(reference/generated/pvlib.iotools.read_solaranywhere: line   23) broken    https://www.solaranywhere.com/support/historical-data/file-formats/ - 520 Server Error:  for url: https://www.solaranywhere.com/support/historical-data/file-formats/
(reference/generated/pvlib.iotools.get_solaranywhere: line   75) broken    https://www.solaranywhere.com/support/data-fields/definitions/ - 520 Server Error:  for url: https://www.solaranywhere.com/support/data-fields/definitions/
(reference/generated/pvlib.iotools.get_solaranywhere: line   69) broken    https://www.solaranywhere.com/support/using-solaranywhere/api/ - 520 Server Error:  for url: https://www.solaranywhere.com/support/using-solaranywhere/api/
(gallery/spectrum/average_photon_energy: line  220) broken    https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.html#pandas.DataFrame - HTTPSConnectionPool(host='pandas.pydata.org', port=443): Max retries exceeded with url: /pandas-docs/stable/reference/api/pandas.DataFrame.html (Caused by SSLError(SSLEOFError(8, 'EOF occurred in violation of protocol (_ssl.c:1006)')))   
(        whatsnew: line   83) broken    https://github.com/Sandia-Labs/PVLIB_Python - 404 Client Error: Not Found for url: https://github.com/Sandia-Labs/PVLIB_Python
(        whatsnew: line   99) broken    https://github.com/bhellis725 - 404 Client Error: Not Found 
for url: https://github.com/bhellis725
(        whatsnew: line   89) broken    https://github.com/johnMoseleyArray - 404 Client Error: Not 
Found for url: https://github.com/johnMoseleyArray
(        whatsnew: line   79) broken    https://github.com/kanderso-nrel - 404 Client Error: Not Found for url: https://github.com/kanderso-nrel
sleeping...
(contributing/introduction_to_contributing: line   54) broken    https://github.com/pvlib/pvlib-python/blob/main/CODE_OF_CONDUCT.md#contributor-covenant-code-of-conduct - Anchor 'contributor-covenant-code-of-conduct' not found

To Reproduce
See this comment. In a nutshell, run the linkcheck Sphinx builder from the command line (working directory of Makefiles in the docs tree).

Expected behavior
N/A

Screenshots
N/A

Versions:

• pvlib.__version__: latest in main at the time of writing

Additional context
Expected links to be updated are related to external documentation pages that complement pvlib's doc pages. Unrelevant links (like broken github users) can be ignored.