ENH: Add **kwargs to pivot_table to allow the specification of aggfunc keyword arguments #57884
Add the option of passing keyword arguments to DataFrame.pivot_table and pivot_table's aggfunc through **kwargs.

- [X] closes #57884 
- [X] Tests added and passed after adding a new feature
- [X] All code checks passed
- [X] Added an entry in the latest `doc/source/whatsnew/v3.0.0.rst` file after adding a new feature.
Thanks @PF2100!