No longer rely on `pkg_resources`

[CommandMC]

As noted in #651, pkg_resources is deprecated and will be removed rather soon. Whipper currently uses it for various things, all of which luckily have alternatives

• Logger plugin discovery is done using importlib.metadata's entry_points - this also makes it easier to install plugins: Simply install them as a regular Python package (python3 setup.py install)
  • I have confirmed whipper-plugin-eaclogger still works fine after installing it with setup.py install. I'm not aware of any other logger plugins that might be tested here
• Version comparison is done using packaging.version. We were already pulling this in with setuptools_scm, so this doesn't really end up changing our dependencies
• Fetching the package version is also done using importlib.metadata, specifically its version function

Closes #651