Make Python stubs generation optional

[olivier-roussel]

This PR adds an option to allow disabling the build of Python stubs (by default stubs will still be generated).
This is useful when cross-compiling as stubs generation needs to use compiled (on host arch) python bindings, making stubs generation tricky to handle.
We typically disable stubs generation on cross-compiled builds for our conda packaging on conda-forge, such as it is commonly done there.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.58%. Comparing base (b7b806c) to head (2580cff).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1890      +/-   ##
==========================================
- Coverage   48.62%   48.58%   -0.04%     
==========================================
  Files         532      532              
  Lines       69293    69293              
  Branches    32402    32402              
==========================================
- Hits        33691    33669      -22     
- Misses      31477    31485       +8     
- Partials     4125     4139      +14     

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