Add support for installation of custom system-chart for turtles

[cpinjani]

Add support for installation of custom system-chart for turtles, in order to test dev/nightly version from 2.13 onward.

Similar reference implementation of hosted providers:

• https://confluence.suse.com/spaces/EN/pages/1271562687/Testing+using+HEAD
• Add setting to skip hosted cluster chart installation rancher#41389

[thehejik]

When rancher is installed with feature flag turtles=false via following helm flags:

--set extraEnv[1].name=CATTLE_FEATURES \
--set-string extraEnv[1].value=turtles=false\,embedded-cluster-api=true

then we are unable to install a custom (using custom helm repo) nor official (using dev-v2.13) turtles chart via Apps.

On attempt to install the chart it says:

k logs helm-operation-55x6k -n cattle-system 
Defaulted container "helm" out of: helm, proxy, init-kubeconfig-volume (init)
helm install --labels=catalog.cattle.io/cluster-repo-name=turtles-chart --namespace=rancher-turtles-system --timeout=10m0s --values=/home/shell/helm/values-rancher-turtles-2025.10.08.yaml --version=2025.10.08 --wait=true rancher-turtles /home/shell/helm/rancher-turtles-2025.10.08.tgz
Error: INSTALLATION FAILED: deployments.apps "rancher-turtles-controller-manager" not found

When watching pods I can see that some turtles resources were created but then they dissapear:

rancher-turtles-system            rancher-turtles-controller-manager-865cb777bf-cxhkt   0/1     ContainerCreating   0          4s
rancher-turtles-system            rancher-turtles-controller-manager-865cb777bf-cxhkt   0/1     Running             0          5s
rancher-turtles-system            rancher-turtles-controller-manager-865cb777bf-cxhkt   0/1     Terminating         0          9s
rancher-turtles-system            rancher-turtles-controller-manager-865cb777bf-cxhkt   1/1     Terminating         0          9s
rancher-turtles-system            rancher-turtles-controller-manager-865cb777bf-cxhkt   0/1     Completed           0          10s
rancher-turtles-system            rancher-turtles-controller-manager-865cb777bf-cxhkt   0/1     Completed           0          10s
rancher-turtles-system            rancher-turtles-controller-manager-865cb777bf-cxhkt   0/1     Completed           0          10s
cattle-system                     helm-operation-zwhjm                                  1/2     Error               0          15s

Problem seems to be that namespace rancher-turtles-system is automatically deleted by rancher when turtles=false.

Edit: reproducer with enabled feature flag turtles=false:

$ kubectl create ns rancher-turtles-system; sleep 30; kubectl get ns rancher-turtles-system
namespace/rancher-turtles-system created
Error from server (NotFound): namespaces "rancher-turtles-system" not found

[thehejik]

The issue with deleting namespace is tracked here #1811