Create system note for alert when issue closing

What does this MR do?

This implements #217686 (closed) and creates a System Note on the Alert, when the corresponding issue is closed.

We already resolve the alert automatically when the issue is closed (added in !33278 (merged)), so this just adds the system note.

• Move closing logic into CloseService, so it can be with other close issue logic.
• Add system note
• Add specs for all changes

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 #217686 (closed)