WHL: Add win32 to build_wheels matrix

[molinav]

This PR extends the GitHub workflow build matrix to include one more item with variables {os: "windows-2019": arch: "auto32", triplet: "x86-windows"}, similarly to the already present win64 build.

• Closes WHL: win32 wheels #1168
• Tests added
  • No new tests, but I checked that the current tests pass on win32 (as run by cibuildwheel).
• Fully documented, including history.rst for all changes and api/*.rst for new API
  • I have not updated history.rst because I was not sure if this addition was that relevant (wheels were already there in pyproj 3.3.1, so this PR simply brings them back).

[codecov]

Codecov Report

Merging #1169 (4849cd1) into main (2a62e36) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1169   +/-   ##
=======================================
  Coverage   96.19%   96.19%           
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  Files          18       18           
  Lines        1707     1707           
=======================================
  Hits         1642     1642           
  Misses         65       65           

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[snowman2]

Thanks @molinav 👍