Reference existing gitlab-operator project for upgrade behavior knowledge, replace functionality within Helm chart

Summary

GitLab's Helm chart has a gitlab-operator sub-chart. This consumes https://gitlab.com/gitlab-org/charts/components/gitlab-operator. The logic from this project should accelerate the patterns for seemless, near zero-downtime upgrades of deployments when managed by this operator.

Details

This project has never come past Alpha, due to a number of complex interactions of the ecosystem over time. The functionality, while reasonably reliable, is very limited and entirely unsupported for customer use (though some do). The ~"Operator" label on gitlab-org/charts/gitlab provides easy access to all of the related issues and work.

It makes sense to move the logic provided within that project here, and pull it out of the Helm chart itself. Even more so, should #1 (closed) come to pass.

Action

This issue can serve as initial discovery, and likely transition to an Epic to break down the various work potions to accomplish the transition.

cc @ljlane @ochienged for project / targets

cc @twk3 @pursultani for insight / reference