Allow migrating a legacy cluster with shared namespaces to separate namespaces per environment
Problem to solve
Any clusters created before https://gitlab.com/gitlab-org/gitlab-ce/issues/52494 are stuck using a single namespace for all project environments.
Proposal
Provide a way for clusters to be "upgraded" to use a separate namespace per environment.
What does success look like, and how can we measure that?
Legacy clusters can be made to use a separate namespace per environment without removing and re-adding the cluster.