Remove deprecated (and removed in 1.19) flag and function --basic-auth-file (#6655)

docs/getting-started.md

docs/vars.md

inventory/sample/group_vars/k8s-cluster/k8s-cluster.yml

roles/kubernetes-apps/ansible/templates/dashboard.yml.j2

roles/kubernetes/master/defaults/main/main.yml

roles/kubernetes/master/tasks/main.yml

roles/kubernetes/master/tasks/users-file.yml

roles/kubernetes/master/templates/known_users.csv.j2

...ubernetes/master/templates/kubeadm-config.v1beta2.yaml.j2

roles/kubespray-defaults/defaults/main.yaml

tests/files/packet_ubuntu18-flannel-containerd-ha-once.yml

tests/files/packet_ubuntu18-flannel-containerd-ha.yml