Replace pkg_resources with importlib

[maxnoe]

closes #6272

[ThiefMaster]

I recommend not putting the issue reference in the commit message itself but only in the PR description. Otherwise it spams one line of being referenced into the issue whenever you rebase and forcepush. Not a big problem but slightly noisy.

[ThiefMaster]

Please run isort indico and fix the linter error (see CI or ruff check and my other comment).

What do you think about using https://pypi.org/project/importlib-metadata/ instead of the stdlib one to avoid any nasty surprises with Python version updates? Or is the API of the stdlib version stable enough now? At least when I moved some of our libraries from setuptools to importlib.metadata, I got some nasty bugs when using the stdlib one on multiple Python versions, that were avoided with importlib-metadata. Of course Indico only supports 3.12 right now, but late this year when 3.13 comes out I plan to add support for it once all our dependencies are compatible, so we will once again be in a situation where differences between the stdlib one may be relevant.

[ThiefMaster]

Thanks, works fine!