Add option for alternative correlation types to `DataFrame.corrwith()`
- [x] closes #21925 
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

This adds a `method` argument to `DataFrame.corrwith()` which calls the corresponding correlation function which already exists within pandas. The default option "pearson" was originally implemented directly in this method, I changed it to match the other options for consistency (and a slight speed improvement).
> The default option "pearson" was originally implemented directly in this method, I changed it to match the other options for consistency (and a slight speed improvement)

Could you demonstrate this speed improvement with the ASV? I am a little dubious that the iterative method is more performant than the existing implementation. 