Update adminGroups GraphQL endpoint to return project statistics

Problem

When the adminGroups GraphQL endpoint was introduced in !202896 (merged), the projectStatistics sub-field was not properly returned. This occurred because the lookahead functionality in ResolvesGroups didn't handle queries with inline fragments (e.g. nodes { ... on Group { projectStatistics } }).

Solution

This MR updates the ResolvesGroup module to properly handle inline fragments by adding the selected_type: ::Types::GroupType argument to the .selects?(:project_statistics) call.

Changes

• Updates the lookahead functionality in ResolvesGroups to correctly detect when projectStatistics is requested in inline fragments
• Ensures the adminGroups GraphQL endpoint returns complete project statistics data
• Adds tests to verify the functionality works as expected

References

Allow read-only access to `Admin Area > Project... (#557844 - closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable read_admin_groups feature flag
2. Login with an admin
3. Go to Admin area groups page and verify that groups display project storage size

# To update the storage size of a project
> Project.find(<project_id>).statistics.update!(storage_size: 100.megabytes)

MR acceptance checklist

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