Fix missing `live_from` when creating audit log

[sentry]

Sentry Issue: FLAGSMITH-API-5D4

TypeError: '<' not supported between instances of 'datetime.datetime' and 'NoneType'
(6 additional frame(s) were not displayed)
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  File "features/workflows/core/models.py", line 198, in create_audit_log_for_related_feature_state
    if self.committed_at < feature_state.live_from:  # type: ignore[operator]

TypeError: '<' not supported between instances of 'datetime.datetime' and 'NoneType'
(20 additional frame(s) were not displayed)
...
  File "features/workflows/core/models.py", line 198, in create_audit_log_for_related_feature_state
    if self.committed_at < feature_state.live_from:  # type: ignore[operator]