feat: support overriding module-dir

[VJftw]

👋 We'd like to be able to add tools available on PyPi and manage their dependencies separately from the rest of our codebase (e.g. semgrep depends on a few modules that we use in the codebase but are incompatibly versioned).

At the moment, it appears we're constrained by the ModuleDir parameter to this plugin where we can only have one repository-wide directory for Python modules.

This PR makes this configurable per python_binary, python_test and python_wheel which enables us to do things like this:

# third_party/python/pipdeptree/BUILD
# The below command works to run `pipdeptree`.
# $ plz run //third_party/python/pipdeptree:pipdeptree

python_wheel(
    name = "pipdeptree",
    version = "2.26.1",
    module_dir = "third_party.python.pipdeptree",
    hashes = ["3849d62a2ed641256afac3058c4f9b85ac4a47e9d8c991ee17a8f3d230c5cffb"],
    binary = True,
    deps = [":packaging", ":pip"],
    licences = ["MIT"],
)

python_wheel(
    name = "packaging",
    hashes = ["5b8f2217dbdbd2f7f384c41c628544e6d52f2d0f53c6d0c3ea61aa5d1d7ff124"],
    licences = [
        "Apache-2.0",
        "BSD-2-Clause",
    ],
    version = "24.1",
)

python_wheel(
    name = "pip",
    hashes = ["a775837439bf5da2c1a0c2fa43d5744854497c689ddbd9344cf3ea6d00598540"],
    licences = ["MIT"],
    version = "24.1",
)

[toastwaffle]

Want to bump the plugin version so this gets released?