Add `cluster_vulnerabilities` feature flag

What does this MR do and why?

Add cluster_vulnerabilities feature flag

• create cluster_vulnerabilities feature flag
• hide Security tab behind it on cluster detail page

Screenshots or screen recordings

Scenario of Cluster Details Page	Feature Flag Off	Feature Flag On
EE w/ Ultimate license
EE w/out Ultimate license		No Visual Change
CE		No Visual Change

How to set up and validate locally

TBD

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 #343911 (closed)