Factor kubectl_apply_stdin into separate "vars only" role

This is needed to make it available to other roles than kubernetes-apps

roles/kubernetes-apps/utils/vars/main.yml

@@ -0,0 +1,12 @@
+---
+_kubectl_apply_stdin:
+- "{{ kubectl }}"
+- apply
+- -f
+- "-"
+- -n
+- "{{ k8s_namespace }}"
+- --server-side="{{ server_side_apply | lower }}"
+# TODO: switch to default SSA
+server_side_apply: false
+kubectl_apply_stdin: "{{ _kubectl_apply_stdin | join(' ') }}"