Use default namespace if it's empty

[FrankYang0529]

harvester/harvester#6098

Using manual install

1. Prepare the terraform rancher provider.tf file
2. Get the kubeconfig file of Harvester and place in the local path
3. Update the provider.tf file with the correct value
   providers.tf.txt
4. Execute following command to trigger terraform to provision RKE2 cluster from Rancer

   $ terraform init
   $ terraform plan
   $ terraform apply
   

5. When RKE2 is stuck in provisioning, get into the server and replace deployment kube-system/harvester-cloud-provider image with frankyang/harvester-cloud-provider:4e1e2347-amd64.
6. Check the RKE2 cluster state

[starbops]

LGTM, thank you!