DOC: Fix validation issues with Index.is_ docstring
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Fix validation issues with the `Index.is_ docstring` and add `Index.identical` to see also section. Trying to finish what was started in #32357 
Yeah, the CI issues are from master branch. The issue that the original PR was hanging on is in "CI / Web and docs" which passed now.