Use a variable for standardizing kubectl invocation (#8329)

* Add kubectl variable

* Replace kubectl usage by kubectl variable in roles

* Remove redundant --kubeconfig on kubectl usage

* Replace unecessary shell usage with command

roles/kubernetes-apps/ingress_controller/cert_manager/tasks/main.yml

@@ -10,8 +10,8 @@
     - upgrade
 
 - name: Cert Manager | Remove legacy namespace
-  shell: |
-    {{ bin_dir }}/kubectl delete namespace {{ cert_manager_namespace }}
+  command: >
+    {{ kubectl }} delete namespace {{ cert_manager_namespace }}
   ignore_errors: true  # noqa ignore-errors
   when:
     - inventory_hostname == groups['kube_control_plane'][0]