This a reproducer for a performance regression of the alert endpoint in the new
UI. The Prometheus instance scrapes a target which generates 6000
debug_alert_ui metrics which then fires 6000 alerts.
Start Prometheus with the new UI
docker-compose up
==> Wait a few secs for alerts to be generated and go to Alerts, this takes
more than 5s to load.
Start Prometheus with the old UI
docker-compose up
==> Wait a few secs for alerts to be generated and go to Alerts, the page is
loaded instantly.