Resolve "Merge or add relation between Alert models"

What does this MR do?

As part of #222253 (closed), we are no longer needing to save PromethusAlertEvents or process them - including creating issues automatically (via IncidentManagement::ProcessPrometheusAlertWorker).

This MR:

• Removes the classes needed to create PromethusAlertEvents (and SelfManagedPrometheusAlertEvents) - Projects::Prometheus::Alerts::CreateEventsService
• Makes the class, responsible for creating/relating and closing issues automatically after an alert was created, do nothing - IncidentManagement::ProcessPrometheusAlertWorker

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry - no needed since the functionality is retained
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• [-] Separation of EE specific content

Part of #222253 (closed)