Add an empty implementation of dsd_pre_inspect()

[ehmatthes]

See dsd 466.

Sample dsd-upsun implementation:

"""Manages all Upsun-specific aspects of the deployment process."""
...

@django_simple_deploy.hookimpl
def dsd_get_plugin_config():
    ...

@django_simple_deploy.hookimpl
def dsd_pre_inspect():
    """Do some work before core inspects the user's project."""
    # There's an apparent bug in the Upsun CLI that causes the .upsun/local/
    # dir to not be ignored on Windows like it is on other OSes. We can fix
    # that ourselves until Upsun updates their CLI.
    # In the configuration-only approach, the user has already run
    # `upsun create`, so we'll try that fix here. This avoids the user running
    # `manage.py deploy` with an unclean Git status.
    if (msg_fixed := upsun_utils.fix_git_exclude_bug()):
        return msg_fixed

...

• Copy this to deploy.py, with a simple pass statement and a longer comment that clarifies when to use the function. Copy that docstring from hookspec?