Only allow group owners to query environment scopes

What does this MR do and why?

Resolves https://gitlab.com/gitlab-org/gitlab/-/issues/418854

This prevents environment scopes to be queried by non-group-owners through GraphQL.

This is to be in-line with our documentation.

How to set up and validate locally

1. Access https://gitlab.com/-/graphql-explorer
2. Execute a query to a group that the requester belongs as Guest user

   query {
     group(fullPath: "group-name") {
       id
       environmentScopes {
         nodes {
           name
         }
       }
     }
   }

3. Confirm that the information is not returned to Guest user.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.