feat: support "update" files for operator descriptions during operator documentation generation

[AnsMelanie]

Take into account operator description updates in MD files named with the _upd suffix, such as op-name_upd.md.
Such files should only contain a section ## Description.

[codecov]

Codecov Report

❌ Patch coverage is 90.47619% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.28%. Comparing base (1e18868) to head (682e74e).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2533       +/-   ##
===========================================
+ Coverage   46.34%   84.28%   +37.93%     
===========================================
  Files          92       92               
  Lines       10819    10855       +36     
===========================================
+ Hits         5014     9149     +4135     
+ Misses       5805     1706     -4099     

[PProfizi]

Conclusion of discussion in meeting:
Change to an update of generate_operators_doc.py as an additional step during doc source generation.

-> generate_operators_doc.py must generate the Markdown sources as used on the Developer Portal.

[github-actions]

Some tests with 'continue-on-error: true' have failed:

• PyDPF-Post API tests on ubuntu-latest

Created by continue-on-error-comment