Include alert source in system note if available

What does this MR do?

For alerts triggered via the generic alert endpoint, this updates the system note to reference the source of the alert. If unavailable, a default string will be used.

Related issue: #250813 (closed)

Screenshots

Payload w/ tool	Rendered	Payload w/o tool	Rendered

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

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done