DOC: add option for skipping execution of code blocks
Came up as an idea at the documentation meeting (https://github.com/pandas-dev/pandas/issues/39183). This should make documentation builds faster for people who aren't working on the code samples.

```
$ time python make.py --single getting_started/comparison/comparison_with_spreadsheets.rst
…
real    0m22.119s
user    0m13.745s
sys     0m1.700s
$ time python make.py --no-ipython --single getting_started/comparison/comparison_with_spreadsheets.rst
…
real    0m17.481s
user    0m11.750s
sys     0m1.521s
```

Very open to alternatives names to `--no-ipython`.

- [ ] ~~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~~

Speeds up full build by 36% in wall clock time.

```
$ python make.py clean && time python make.py html --num-jobs 4
…
real    7m51.219s
user    17m35.420s
sys     1m10.225s
$ python make.py clean && time python make.py html --no-ipython --num-jobs 4
…
real    5m1.531s
user    13m12.087s
sys     0m45.678s
```

Ran these in GitHub Codespaces. status here? On second thought, not sure it's worth the added complexity for the narrow use case. If someone disagrees, happy to reopen and fix. Thanks for the reviews!