REF: add skeleton for strategy pattern in describe
- [ ] xref #36833
- [ ] 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

Added a skeleton for the strategy pattern in ``pandas/core/describe.py``.
Currently the methods ``describe`` simply delegate to the corresponding ``describe_`` functions.
In the next steps I plan on moving the ``describe`` functions into each of the strategy classes.
Finally, these functions can be unified, since a lot there has a common pattern.