Add tooltip to validity check

What does this MR do and why?

This adds tooltip to the validity check in the vulnerability report page.

🚨 Please note this feature is still WIP, there is no API integration. The vulnerability report will not update when validity check is selected. That will be tackled in another MR > Draft: API integration for filter by validity c... (!203851)

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable FF: http://gdk.test:3000/rails/features/advanced_vulnerability_management
2. Enable FF: http://gdk.test:3000/rails/features/validity_check_es_filter
3. Disable FF: http://gdk.test:3000/rails/features/vulnerability_report_filtered_search_v2
4. Clone this project: https://gitlab.com/gitlab-org/govern/threat-insights-demos/frontend/validity-checks
5. Run a successful pipeline
6. Go to the vulnerability report
7. Select the validity check in the search bar. Notice the tooltip.

Please note the filter doesn't work yet. The validity check is UI only.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #557869 (closed)