Show checkboxes on the cluster agent vuln list

What does this MR do and why?

Show checkboxes on the cluster agent vuln list

• the vulnerabiity list allows for bulk actions
• the checkboxes were hidden, but they should be shown
• fix bug where the selected summary was not appearing

Screenshots or screen recordings

Before	After
	Checkboxes can be turned off or on!

How to set up and validate locally

1. Ensure your GDK has a GitLab Ultimate license
2. Ensure your GDK is connected to the GitLab Runner
3. Follow these docs to set up the kubernetes agent
4. Navigate to a project
5. Link the agent to a project
6. Enable the :cluster_vulnerabilities feature flag
7. Navigate to the agent
8. View the vulnerabilities

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.

Related to #350206 (closed)