Redis N+1 in /api/v4/groups/:id/projects - open issues count key

Issue that derives from #214510 (closed)

One of a redis keys cache:gitlab:projects/count_service/$NUMBER/$NUMBER/public_open_issues_count is called in the loop. It is caused by this place: https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/services/projects/open_issues_count_service.rb - I wonder how we can effectively refactor it since user can have different roles in different projects.