Migrate managed clusters that aren't using managed features to unmanaged

Problem to solve

There are project level clusters that were created before #56557 (closed) that GitLab considers managed, but are actually being managed by users. This means we cannot enable just-in-time resource creation for these clusters, as deployment jobs for these projects would fail when GitLab tries to create the "managed" resources. If these clusters are set to unmanaged, we can enable just-in-time resource creation for all clusters, and remove legacy logic that creates resources as soon as a cluster is added to a project.

Proposal

Find all clusters that are mistakenly marked as managed, and set them to unmanaged.

Possible strategies for finding relevant clusters:

• All managed, project-level clusters that have a successful deployment, and do not have a kubernetes_namespace record persisted for the project.

• ?

Caveats

Unless we can be 100% accurate with our migration, we will need to implement https://gitlab.com/gitlab-org/gitlab-ce/issues/60617 first, so that users can make this change themselves.

What does success look like, and how can we measure that?

just-in-time resource creation is enabled for all clusters.

Links / references