Add an empty implementation of dsd_pre_inspect()

See [dsd 466](https://github.com/django-simple-deploy/django-simple-deploy/issues/466).

Sample dsd-upsun implementation:

```python
"""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?