Use note header component in event item component

NOTE: This MR requires that !28898 (merged) be merged first.

What does this MR do?

Throughout the first class vulnerabilities feature, we have a common header for a system note. It can either be a single line:

Single line system note

or on two lines where the top line is the header:

Two line system note

There is already a app/assets/javascripts/notes/components/note_header.vue component that provides the header and handles some special cases. This MR is to switch history_entry.vue to use note_header.vue instead of duplicating what it does. It also makes some changes to note_header.vue to make it more flexible and reusable.

How to test locally

https://gitlab.com/snippets/1956676

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