Fix kubeconfig variable to support both playbook and scenario usage

The federation_manager_kubeconfig variable now falls back to kubeconfig_output_dir
if kind_config_dir is not defined. This allows the roles to work in both scenarios:

- Playbooks (deploy.yml): Set kind_config_dir in pre_tasks
- Scenarios (deploy_quick_single_oop.yml): Only set kubeconfig_output_dir

Tested with deploy_quick_single_oop.yml - all components deployed successfully.