Fix auto-schema generation for nested config entries with _target_

[lebrice]

The auto-schema generation for nested config entries with a _target_ was not working correctly. This pull request fixes the issue by properly handling nested entries and generating the schema based on the target signature. Additionally, a description is added to the generated schema to indicate that it is based on the signature of the target.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.40%. Comparing base (32ae062) to head (e85bf3e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
- Coverage   70.72%   70.40%   -0.32%     
==========================================
  Files          57       58       +1     
  Lines        3593     3589       -4     
==========================================
- Hits         2541     2527      -14     
- Misses       1052     1062      +10     

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