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.
ee/clickhouse/process_event.py
import datetime
import json
from typing import Dict, Optional
from uuid import UUID
import statsd
from dateutil import parser
from dateutil.relativedelta import relativedelta
from django.conf import settings
from django.db.utils import IntegrityError
from sentry_sdk import capture_exception
from ee.clickhouse.models.event import create_event
from ee.clickhouse.models.session_recording_event import create_session_recording_event
from ee.kafka_client.client import KafkaProducer
from ee.kafka_client.topics import KAFKA_EVENTS_WAL
from posthog.ee import is_ee_enabled
from posthog.models.element import Element
from posthog.models.person import Person
from posthog.models.team import Team
from posthog.models.utils import UUIDT
from posthog.tasks.process_event import (
    _add_missing_feature_flags,
    handle_identify_or_alias,
    sanitize_event_name,
    store_names_and_properties,
)
if settings.STATSD_HOST is not None:
    statsd.Connection.set_defaults(host=settings.STATSD_HOST, port=settings.STATSD_PORT)
def _capture_ee(