Guard security dashboard risk score by project behind feature flag

What does this MR do and why?

Guard security dashboard risk score by project behind feature flag

This guards the project grouping on the risk score panel on the new security dashboard behind a derisk feature flag for performance considerations.

References

Related #579448

Screenshots or screen recordings

feature flag disabled	feature flag enabled

How to set up and validate locally

1. With feature flag group_vulnerability_risk_scores_by_project disabled, go to group level new security dashboard
2. Validate it does not show the grouping buttons
3. Add ?riskScore.groupBy=project to the URL and refresh. Validate it still does not show the group by buttons and not the project heat map
4. Enable the feature flag http://gdk.test:3000/rails/features/group_vulnerability_risk_scores_by_project
5. Visit the security dashboard and validate it is showing the group by buttons

MR acceptance checklist

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