Add enrollment alert data GCS reader and Celery fetch task

[data-sync-user]

What to do

Fetch enrollment data from GCS and update experiments daily at 8am.

Location: experimenter/experimenter/jetstream/

Deliverables

• Add to client.py:

ENROLLMENT_ALERTS_FOLDER = "enrollment_alerts"

def get_enrollment_alert_data():
    """Fetch from GCS path: enrollment_alerts/enrollment_alerts_latest.json"""

• Add to tasks.py:

@app.task
@metrics.timer_decorator("fetch_enrollment_alert_data")
def fetch_enrollment_alert_data():
    """Fetch data, update all experiments' enrollment_alert_data field"""

• Add to settings.py (CELERY_BEAT_SCHEDULE):

"fetch_enrollment_alert_data": {
    "task": "experimenter.jetstream.tasks.fetch_enrollment_alert_data",
    "schedule": crontab(minute=0, hour=8),  # 8am UTC daily
}

• Add metrics: started, completed, failed
• Add logging and error handling

Acceptance Criteria

• Reader fetches from GCS successfully
• Task updates experiments' enrollment_alert_data field
• Scheduled for 8am UTC daily (after 3am ETL)
• Metrics increment correctly
• Error handling in place

┆Issue is synchronized with this Jira Task