Fix custom_cni manifest apply failure for multi-namespace resources (#13091)

* fix(custom_cni): make namespace optional

Keep kube-system as the default for existing manifests. An empty custom_cni_namespace omits kubectl's namespace flag so manifests spanning multiple namespaces can be applied without changing legacy behavior.

Signed-off-by: Kay Yan <kay.yan@daocloud.io>

* docs(custom_cni): document multi-namespace manifests

Signed-off-by: Kay Yan <kay.yan@daocloud.io>

---------

Signed-off-by: Kay Yan <kay.yan@daocloud.io>

roles/network_plugin/custom_cni/defaults/main.yml

@@ -1,6 +1,7 @@
 ---
 
 custom_cni_manifests: []
+custom_cni_namespace: kube-system
 
 custom_cni_chart_namespace: kube-system
 custom_cni_chart_release_name: ""

roles/network_plugin/custom_cni/tasks/main.yml

@@ -19,7 +19,7 @@
 
   - name: Custom CNI | Start Resources
     kube:
-      namespace: "kube-system"
+      namespace: "{{ custom_cni_namespace | default(omit, true) }}"
       kubectl: "{{ bin_dir }}/kubectl"
       filename: "{{ kube_config_dir }}/{{ item | basename | replace('.j2', '') }}"
       state: "latest"