Replace pkg_resources with importlib_metadata

[jakirkham]

Currently pkg_resources is used in a few places (in particular iter_entry_points). Would be good to replace this with importlib_metadata (importlib.metadata added in Python 3.8 & stable in Python 3.10), which supersedes pkg_resources. In particular usages of iter_entry_points can be replaced by entry_points.

This also would allow setuptools to be dropped as a runtime requirement.

[jakirkham]

FWIW a similar change was made in Distributed recently ( dask/distributed#5923 ). Maybe provides a better idea how this might look here

[philippjfr]

Thanks @jakirkham, we do still support Python 3.7 for the time being so I'm not sure we can switch quite yet.

[jakirkham]

Right the backport package supports Python 3.7