vllm: ensure kdevops_workflow_enable_vllm is defined

output yaml in Kconfig will not generate the variable if it's behind
a conditional. Add it to the default playbook variables so it's always
available.

Signed-off-by: Daniel Gomez <da.gomez@samsung.com>

Author: dagomez137

playbooks/roles/vllm/defaults/main.yml

@@ -15,3 +15,5 @@ vllm_engine_image_repo: "{{ 'openeuler/vllm-cpu' if vllm_use_cpu_inference | def
 vllm_engine_image_tag: "{{ 'latest' if vllm_use_cpu_inference | default(false) else 'v0.10.2' }}"
 vllm_prod_stack_router_image: ghcr.io/vllm-project/production-stack/router
 vllm_prod_stack_router_tag: latest
+
+kdevops_workflow_enable_vllm: false