Turn off Group and Stage Throughput Charts in Insights

Proposal

The different project reporting populations with is_part_of_product creates confusion with Throughput on Group and Stage dashboards differences: https://gitlab.com/gitlab-data/analytics/-/merge_requests/2354#note_286415675

• Remove group/stage Throughput charts
• Add guidance to handbook for go forward sources to https://about.gitlab.com/handbook/engineering/management/engineering-metrics/
• Add a link in Insights to handbook guidance for Throughput

Discuss

• Should we turn off any of the Bug Reports with a link to https://app.periscopedata.com/app/gitlab/576726/GitLab-Bugs?
• Are there other reports that we should remove as apart of #116