Release of #1700. The following lines need to be added to posthog/celery.py to release PR. Deliberately excluded to manually test the PR without sending everyone an email.

```python
# inside setup_periodic_tasks
sender.add_periodic_task(
    crontab(day_of_week="mon"), task_weekly_email_report.s(),
)

# bottom of file
@app.task
def task_weekly_email_report(self):
    from posthog.tasks.email import send_weekly_email_report

    send_weekly_email_report()
```
posthog/celery.py
import os
import time
import posthoganalytics
import redis
import statsd  
from celery import Celery
from celery.schedules import crontab
from django.conf import settings
from django.db import connection
os.environ.setdefault("DJANGO_SETTINGS_MODULE", "posthog.settings")
app = Celery("posthog")
app.config_from_object("django.conf:settings", namespace="CELERY")
app.autodiscover_tasks()
app.conf.broker_pool_limit = 0
redis_instance = redis.from_url(settings.REDIS_URL, db=0)
ACTION_EVENT_MAPPING_INTERVAL_MINUTES = 10
statsd.Connection.set_defaults(host=settings.STATSD_HOST, port=settings.STATSD_PORT)
@app.on_after_configure.connect
def setup_periodic_tasks(sender, **kwargs):