DOC: update array-like parameters if scalars accepted
- [x] based on discussion in #41807 
- [x] tests added / passed
  - N/A since only doc changes
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
  - N/A since only doc changes
- [x] whatsnew entry
  - Not needed

Based on discussion, I went through all docstrings that had the regex `":.*array-like"` and added a scalar as an accepted argument where appropriate.

