DOC: Upload cheatsheets to site
- [x] closes #40949
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry


I went ahead and modified the `.github/workflows/ci.yml` so that the cheatsheets are copied to the docs build directory once the Sphinx site is built
cc @Dr-Irv @datapythonista over to you Thanks @trallard, really nice.

The CI for this commit (PR merge) will update the website, and the cheatsheet in https://pandas.pydata.org/Pandas_Cheat_Sheet.pdf should be updated with the new version. The new cheatsheet contains 3 columns instead of two for the "Subset" sections, in the bottom right part of the first page. In 30 minutes or so we should see the change. If the job fails, the cheatseet is not replaced, or whatever, we'll follow up with another PR. There is no easy way to test this further without merging the PR.

Note that the copying of the cheatsheet to the directory to upload was already being run in this PR. So the job shouldn't be failing. It's just the upload that hasn't been tested already. Ups, just realized now that we're copying the cheatsheets to the directory after the directory is uploaded, so the cheatsheets won't be pushed, and will be delete from the server, my bad. I'll open a PR to fix it.