Advise about troubleshooting Elasticsearch overloading Sidekiq

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/122874



Merged-by: Ashraf Khamis <akhamis@gitlab.com>
Approved-by: Ashraf Khamis <akhamis@gitlab.com>
Co-authored-by: Katrin Leinweber <kleinweber@gitlab.com>