Add enabled to pkgs to handle ipvs

Some packages requirements depends on inventory variables
(`kube_proxy_mode` in that case but it could apply to others).

As the case seems pretty rare, instead of adding complexity to pkgs, we
add an escape hatch to use jinja conditions.
That should be revisited if we find ourselves shoehorning lots of logic
in this later on.

roles/kubernetes/preinstall/vars/main.yml

@@ -54,7 +54,15 @@ pkgs:
           major_versions:
           - "11"
           - "12"
+  ipset:
+    enabled: "{{ kube_proxy_mode != 'ipvs' }}"
+    groups:
+    - k8s_cluster
   iptables: *deb_redhat
+  ipvsadm:
+    enabled: "{{ kube_proxy_mode == 'ipvs' }}"
+    groups:
+    - k8s_cluster
   libseccomp: *redhat_family
   libseccomp2:
     groups: