Backport PR #3672 on branch 1.11.x (Settings docs overhaul)

[flying-sheep]

Backports #3672

[codecov]

Codecov Report

❌ Patch coverage is 83.05785% with 41 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.72%. Comparing base (6c18805) to head (589289e).
⚠️ Report is 28 commits behind head on 1.11.x.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/scanpy/_settings.py	88.05%	24 Missing ⚠️
src/scanpy/_singleton.py	46.87%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           1.11.x    #3680      +/-   ##
==========================================
- Coverage   74.83%   74.72%   -0.12%     
==========================================
  Files         115      117       +2     
  Lines       13207    13307     +100     
==========================================
+ Hits         9884     9943      +59     
- Misses       3323     3364      +41     

Files with missing lines	Coverage Δ
src/scanpy/__init__.py	96.00% <100.00%> (ø)
src/scanpy/_types.py	100.00% <100.00%> (ø)
src/scanpy/_utils/__init__.py	76.95% <100.00%> (+0.04%)	⬆️
src/scanpy/datasets/_datasets.py	100.00% <ø> (ø)
src/scanpy/datasets/_ebi_expression_atlas.py	94.73% <ø> (ø)
src/scanpy/external/pp/_mnn_correct.py	22.22% <ø> (ø)
src/scanpy/external/tl/_phate.py	39.13% <ø> (ø)
src/scanpy/logging.py	97.34% <100.00%> (-0.05%)	⬇️
src/scanpy/neighbors/_doc.py	100.00% <ø> (ø)
src/scanpy/plotting/_rcmod.py	100.00% <ø> (ø)
... and 5 more