Add #resolved_on_default_branch to Vulnerability

What does this MR do?

Add resolved_on_default_branch key to Vulnerability entity presenter as per #207182 (closed). This is a part of changes required for #35860 (closed)

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.