secureDnsMode
Can be 'off', 'automatic' or 'secure'. Configures the DNS-over-HTTP mode. When 'off', no DoH lookups will be performed. When 'automatic', DoH lookups will be performed first if DoH is available, and insecure DNS lookups will be performed as a fallback. When 'secure', only DoH lookups will be performed. Defaults to 'automatic'.