add extras for hatchling and setuptools

[alexrashed]

Motivation

The hatchling build tool integration has just been merged with #35.
With build isolation, hatchling is not in the actual environment being used for the project but only in the temporary environment created by the build environment. (Actually, this is also the case for setuptools, but setuptools is often defined by transitive dependencies - f.e. packaging depends on setuptools.)
When using the entrypoints command, you would end up with the following error (if you are using hatchling as build backend in the pyproject.toml but do not have it in your dependencies):

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/ls/Repos/plux/plux/__main__.py", line 13, in <module>
    main()
    ~~~~^^
  File "/home/ls/Repos/plux/plux/__main__.py", line 9, in main
    cli.main(argv)
    ~~~~~~~~^^^^^^
  File "/home/ls/Repos/plux/plux/cli/cli.py", line 183, in main
    args.func(args)
    ~~~~~~~~~^^^^^^
  File "/home/ls/Repos/plux/plux/cli/cli.py", line 41, in entrypoints
    project = _load_project(args)
  File "/home/ls/Repos/plux/plux/cli/cli.py", line 31, in _load_project
    from plux.build.hatchling import HatchlingProject
  File "/home/ls/Repos/plux/plux/build/hatchling.py", line 15, in <module>
    from hatchling.builders.config import BuilderConfig
ModuleNotFoundError: No module named 'hatchling'

Changes

• This PR adds two extras, such that you can define the build backend you want the transitive dependencyies of:
  • setuptools and
  • hatchling

[thrau]

Thanks Alex! Classic case of "it was working on my machine". Adding two extras is a good idea

[dfangl]

Makes sense!