Changes:
- Fix dangerous default argument {} used in posthog/urls.py
- Remove unnecessary list comprehension in posthog/api/funnel.py
- Remove redundant import `Funnel` in posthog/api/funnel.py
- Use `in` instead of multiple comparions in posthog/api/action.py,
posthog/api/event.py, and posthog/models.py
Also added .deepsource.toml file to configure and run continuous static
analysis with DeepSource.
