Handle deprecation of pkg_resources and favor importlib

[jacebrowning]

Specifically, the Python 3.10 images on CircleCI no longer include pkg_resrouces as it's deprecated:

$ honcho start
Traceback (most recent call last):
  File "/home/circleci/myproject/.venv/bin/honcho", line 5, in <module>
    from honcho.command import main
  File "/home/circleci/myproject/.venv/lib/python3.10/site-packages/honcho/command.py", line 10, in <module>
    from pkg_resources import iter_entry_points
ModuleNotFoundError: No module named 'pkg_resources'

Starting in Python 3.8, importlib.metdata is the preferred way to find entry points.

[RealOrangeOne]

pkg_resources is no longer included in virtual environments from Python 3.12 - making this PR required to run on 3.12.

Alternatively, manually installing setuptools (pip install setuptools) also solves the problem.

@nickstenning as this is going to slowly start becoming more of an issue - any chance of a release? 🙂

[asottile-sentry]

this should really be flipped -- prefer importlib.metadata and if it's not available then fall back to (deprecated) pkg_resources -- otherwise this will still trigger deprecation warnings even on systems where importlib.metadata would avoid such warnings