PEP 420 native namespace

[gforcada]

Part of plone/Products.CMFPlone#3928

---

📚 Documentation preview 📚: https://ploneapi--588.org.readthedocs.build/

[mister-roboto]

@gforcada thanks for creating this Pull Request and helping to improve Plone!

TL;DR: Finish pushing changes, pass all other checks, then paste a comment:

@jenkins-plone-org please run jobs

To ensure that these changes do not break other parts of Plone, the Plone test suite matrix needs to pass, but it takes 30-60 min. Other CI checks are usually much faster and the Plone Jenkins resources are limited, so when done pushing changes and all other checks pass either start all Jenkins PR jobs yourself, or simply add the comment above in this PR to start all the jobs automatically.

Happy hacking!

[davisagli]

Tests are failing:

   Traceback (most recent call last):
    File "/home/runner/work/plone.api/plone.api/.tox/py311-plone60/lib/python3.11/site-packages/zc/buildout/buildout.py", line 2323, in main
      buildout = Buildout(config_file, options,
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/home/runner/work/plone.api/plone.api/.tox/py311-plone60/lib/python3.11/site-packages/zc/buildout/buildout.py", line 370, in __init__
      cfg_data, _ = _open(
                    ^^^^^^
    File "/home/runner/work/plone.api/plone.api/.tox/py311-plone60/lib/python3.11/site-packages/zc/buildout/buildout.py", line 1876, in _open
      fp = open(filename)
           ^^^^^^^^^^^^^^
  IsADirectoryError: [Errno 21] Is a directory: '//home/runner/work/plone.api/plone.api'