* Add kubeadm_join_phases_skip variable

* Update kubeadm_join_phases_skip comment

Co-authored-by: Cristian Calin <6627509+cristicalin@users.noreply.github.com>

* Add kubeadm_join_phases_skip_default variable to follow the same logic with kubeadm_init_phases_skip

Co-authored-by: Cristian Calin <6627509+cristicalin@users.noreply.github.com>