EKS - unable to remove all managed nodegroups from imported EKS cluster that also has self-managed nodes

[mantis-toboggan-md]

Blocked by the open PR https://github.com/rancher/dashboard/pull/11294

This will need to be done in tandem with a backend fix https://github.com/rancher/rancher/issues/45972. The UI needs to be able to send an empty array for <norman cluster>.eksConfig.nodeGroups to delete the nodeGroups (setting to null wont work because of the kontainer driver syncing mechanism; when fields are null whatever is in the upstream spec will be used instead). Currently, there is norman API validation which prevents sending an empty array.