Schedule update for prometheus after alert creation

What does this MR do?

This fixes the case where alerts aren't created automatically after Prometheus is installed in a Project for the first time.

It schedules a Prometheus update after the default alerts have been created.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #216735 (closed)