Don't load admin groups from controller action

What does this MR do and why?

Related to Migrate admin area groups list to Vue shared co... (&17783 - closed)

As part of an initiative to align group and project list UX across the product we are moving Admin -> Groups from HAML/vanilla JS to Vue. The Vue version is behind the admin_groups_vue feature flag and loads groups via a GraphQL query. To avoid duplicate queries when the admin_groups_vue FF is enabled we are adding a check to Admin::GroupsController#index action.

References

Screenshots or screen recordings

No visual changes

How to set up and validate locally

1. Go to /rails/features and enable admin_groups_vue feature flag
2. Open performance bar (p + b) and go to /admin/groups. There shouldn't be any group queries in the initial load.

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