Rancher run system-upgrade even though the managed-system-upgrade-controller is disabled

Similar to this old issue :

Although managed-system-upgrade-controller is disabled, Rancher continues attempting to install the system-upgrade Helm chart. The chart fails to install due to CIS compliance violations, causing the controller to retry indefinitely.

As mentioned in old issue #2498 (closed), we don't need this feature in Sylva.

According Rancher documentation ( https://ranchermanager.docs.rancher.com/getting-started/installation-and-upgrade/installation-references/feature-flags), the setting imported-cluster-version-management must now also be set to false in Rancher settings to fully disable it.