MOVE: describe to pandas/core/describe.py
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

Move ``describe`` functionality to a separate module and prepare for the further refactor/simplification (xref #36833).

 - Created new module ``pandas/core/describe.py``
 - Delegate the functionality of ``NDFrame.describe`` to function ``describe_ndframe`` in the new module