Design and implement RBAC switcher

[kvaps]

Following up https://github.com/aenix-io/etcd-operator/issues/76

We need to implement flag that enables or disables mTLS auth in etcd, the way it is doing Kamaji:

if etcdctl user get root &>/dev/null; then
  echo "User already exists, nothing to do"
else
  etcdctl user add --no-password=true root &&
  etcdctl role add root &&
  etcdctl user grant-role root root &&
  etcdctl auth enable
fi