DOC #62437 Replace @Substitution and @Appender

[josquinlarsen]

for file: pandas/core/groupby/groupby.py

• contributes to closing DOC: Replace @Appender, @Substitution, @doc with inlined docstrings #62437
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.
• If I used AI to develop this pull request, I prompted it to follow AGENTS.md.

[rhshadrach]

lgtm

[rhshadrach]

Thanks for the PR! pre-commit build is failing - the format needs to be fixed.

[josquinlarsen]

I was having issues fixing my original PR. I've created a new one (#63234) that is passing the pre-commit checks and will close this one