Replace the use of `pkg_resources` with `importlib.metadata`

[radez]

This patch replaces references to pkg_resources with importlib.metadata The latest setuptools emits the following warning: DeprecationWarning: pkg_resources is deprecated as an API.

What kind of change does this PR introduce?

• [ ] bug fix
• [ ] feature
• [x] docs update
• [x] tests/coverage improvement
• [ ] refactoring
• [x] other

What is the related issue number (starting with #) Fixes #1973

Checklist:

• [x] I think the code is well written
• [x] I wrote good commit messages
• [x] I have squashed related commits together after the changes have been approved
• [x] Unit tests for the changes exist
• [x] Integration tests for the changes exist (if applicable)
• [x] I used the same coding conventions as the rest of the project
• [x] The new code doesn't generate linter offenses
• [x] Documentation reflects the changes
• [x] The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences

[webknjaz]

@radez together with this, please drop setuptools as a testing dep: https://github.com/cherrypy/cherrypy/blob/8946187/setup.py#L101C14-L101C24

[radez]

@radez together with this, please drop setuptools as a testing dep: https://github.com/cherrypy/cherrypy/blob/8946187/setup.py#L101C14-L101C24

Done