[Python][R][Docs] Update the "Integrating PyArrow with R" documentation section to not use `_import_from_c`/`_export_to_c`

[jorisvandenbossche]

Currently, the "Integrating PyArrow with R" page (https://arrow.apache.org/docs/13.0/python/integration/python_r.html) has a section on using the C Data Interface to communicate data between R and Python. This section uses the low-level _import_from_c / _export_to_c methods, and we should see if we can and should update this to not use those methods directly.

[jorisvandenbossche]

I wanted to point to the existence of rpy2-arrow, which already implements the C Data Interface, but so looking at that page again, we actually already do use that for the main example. The additional section https://arrow.apache.org/docs/13.0/python/integration/python_r.html#r-to-python-communication-using-the-c-data-interface is then to "switch from using rpy2-arrow to using the plain C Data interface".

I am not sure how important this is that we point users towards such a solution, though. And if we want to keep this "advanced" low-level example that doesn't use rpy2-arrow, for such a section it might also be fine to use the lower-level methods instead of the PyCapsule protocol.
(although currently if an error happens in the R function, that's a memory leak?)