Migrate from pkg_resources to importlib or backports

[stevepiercy]

From https://setuptools.pypa.io/en/latest/pkg_resources.html

Caution

Use of pkg_resources is deprecated in favor of importlib.resources, importlib.metadata and their backports (importlib_resources, importlib_metadata). Some useful APIs are also provided by packaging (e.g. requirements and version parsing). Users should refrain from new usage of pkg_resources and should work to port to importlib-based solutions.

It might be good to drop EOLed Python versions at the same time.

Whenever this issue is resolved, then I can remove the setuptools requirement in this PR: plone/plone.restapi#1815.

[stevepiercy]

@datakurre do you know how to fix this? Sphinx is getting louder.

https://github.com/plone/documentation/actions/runs/19815915650/job/56767027241#step:5:973

/home/runner/work/documentation/documentation/venv/lib/python3.12/site-packages/sphinxcontrib/httpexample/utils.py:5: UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.