Refs #24020 -- return expressions from get_group_by_cols()
Fixed #23788 (2) -- Improved gettext version checker

Thanks Tim Graham for the report and initial patch.
Removed need to update Python version support note on each new release.
Forward-ported test and release note from f46a16614

Refs #24015.
Moved version directives to the bottom of the loaddata section.
Used the :ticket: syntax more extensively
Used https for most *.python.org links
Updated some other external links in the docs
Made model_regress unpickling test CWD-independent

Refs #24007. Thanks Tim Graham for his help with the patch.
Fixed refs #24007 test on Windows.
Added words to docs wordlist.
Added upgrade instructions for deprecated model _meta permission methods.
Added RasterSource/GDALBand GDAL objects

Based on Daniel Wiesmann's raster branch. Thanks Daniel Wiesmann
and Tim Graham for the reviews. Refs #23804.