DOC: Move general utility functions to better locations
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).

There was `doc/source/reference/general_functions.rst` and `doc/source/reference/general_utility_functions.rst`

So split `doc/source/reference/general_utility_functions.rst` into appropriate sections



great