add documentation for BadCredentialsException

[Lslightly]

add documentations for easier root cause localization. Summary for #1753 and #2955

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.73%. Comparing base (7266e81) to head (4f89110).
Report is 1 commits behind head on main.

❗ Current head 4f89110 differs from pull request most recent head 1fadb37

Please upload reports for the commit 1fadb37 to get more accurate results.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2973      +/-   ##
==========================================
- Coverage   96.74%   96.73%   -0.02%     
==========================================
  Files         147      147              
  Lines       14978    14984       +6     
==========================================
+ Hits        14491    14495       +4     
- Misses        487      489       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Lslightly]

I find bad looks in readthedocs but I am not familiar with readthedocs.

But the headings work well in vscode python extension when hovering over BadCredentialsException.

[EnricoMi]

I'd suggest the following improvements in these instructions.