Change feature flag permission to be group

What does this MR do and why?

Changing the feature flag to be group, which will make it possible to enable it with chatops via the --group flag. The current project flag doesn't work b/c the vulnerability page is on the group level

/chatops run feature set --group=gitlab-org/govern/threat-insights-demos/frontend refactor_vulnerability_tool_filter true

Screenshots or screen recordings

There is no UI/UX change in this MR

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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