Adds artifact CDN storage detail

John Jarvisrequested to merge
jarv/add-artifacts-cdn-detail into master

This adds some more detailed panels for the artifacts CDN, sourced from the stackdriver exporter.

https://dashboards.gitlab.net/dashboard/snapshot/WwGXHp3uQtSYr4uDfjYLGGh78ACCMzlC

Part of https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16466

Edited by John Jarvis

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