WIP: Add the option to choose if a cluster is managed by GitLab

What does this MR do?

This MR adds the ability to define whether a Kubernetes cluster namespace/service account is managed by GitLab.

Creation

• On creation, a user can choose whether their cluster is managed by GitLab or not.

Cluster settings

• A user can see whether GitLab is managing their cluster within the cluster settings but this setting is disabled and not editable by the user.

What are the relevant issue numbers?

Closes #56557 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides