Create load generator for webpush

[spikecurtis]

Goal:

• To observe how Coder handles web push notification usage at scale.

User target	coderd replicas	Subscribed users	Notification frequency
1k	3	200	6/minute
2k	3	400	6/minute
3k	4	600	6/minute
10k	10	2000	6/minute

Implementation:

• Tools:
  • coder scaletest command for bulk creating users.
  • Fake web push service that records requests from coderd.
  • API Clients to bulk create web push subscriptions, and spawn test notifications.

Run Sequence:

1. Create users
2. Have each user client subscribe to webpush notifications.
3. Establish baseline (10 minutes).
4. Have each user client spawn a test notification every 10 seconds.
5. Run for 10-15 minutes.

Key Results:

• Time until the notification is received by the fake web push service.
• If any notifications were missed altogether.

Other Results

• Coder deployment + database resource utilization (incl. pprofs, Grafana Pyroscope)