Move NotificationService#prometheus_alerts_fired and its dependencies from EE to CE
Summary
Contributes to #42640 (closed)
Move NotificationService#prometheus_alerts_fired, and Mailer::Projects#prometheus_alert_fired_email from EE domain to CE.
Improvements
Moving Prometheus alerts from EE to CE requires a lot of code changes. All the required changes can be split and moved in several steps (as described here).