posthog-js supports person.set_once but our backend doesn't. Make sure we can pass through `$set_once` on an `$identify` call, and only set the properties within if the properties aren't already set on the user.
posthog/tasks/process_event.py
import datetime
import json
from numbers import Number
from typing import Any, Dict, List, Optional, Tuple, Union
import posthoganalytics
from celery import shared_task
from dateutil import parser
from dateutil.relativedelta import relativedelta
from django.db import IntegrityError
from sentry_sdk import capture_exception
from posthog.models import Element, Event, Person, SessionRecordingEvent, Team
from posthog.models.feature_flag import FeatureFlag, get_active_feature_flags
def _alias(previous_distinct_id: str, distinct_id: str, team_id: int, retry_if_failed: bool = True,) -> None: