Expose `vulnerability_events` field in REST integrations API endpoints

What does this MR do and why?

The vulnerability events have been around since 14.3 49e788b9 but was previously missing from integration API responses. This change exposes the field in the integrations API.

How to set up and validate locally

Visit the integrations API endpoints:

• http://gdk.test:3000/api/v4/projects/<project_id>/integrations?private_token=<private_token>
• http://gdk.test:3000/api/v4/projects/<project_id>/integrations/jenkins?private_token=<private_token> (or any individual integration endpoint)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.