Adds runbook for error tracking

John Jarvisrequested to merge
jarv/runbook-errortracking into master

For the open beta rollout of Opstrace ErrorTracking, this create the scaffolding for the service to aid the oncall if there are issues.

Part of gitlab-com/gl-infra/production#7586 (closed)

At this time there is no support for this service, no SLAs, until it reaches GA.

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