Rollout of pending builds parity

Summary

This issue is to rollout the feature on production, that is currently behind the ci_pending_builds_queue_maintain feature flag.

Owners

• Team: ~"group::continuous integration"
• Most appropriate slack channel to reach out to: #g_ci
• Best individual to reach out to: @grzesiek
• PM: @jreporter

The Rollout Plan

• Full rollout and verification on staging
• Full rollout to grzesiek/ci-cd-sandbox on production
• Full rollout to gitlab-org/gitlab on production
• 10% rollout on gitlab.com
• 25% rollout on gitlab.com
• 50% rollout on gitlab.com
• 100% rollout on gitlab.com

Expectations

What are we expecting to happen?

Builds being created and processed correctly.

What can we monitor to detect problems with this?

https://dashboards.gitlab.net/d/stage-groups-continuous_integration/stage-groups-group-dashboard-verify-continuous-integration