Implement Secure Zero Touch Provisioning options (RFC8572)

There's RFC8572 published that introduces two SZTP Redirect Options, one for DHCPv4 and one for DHCPv6. My brief look at them suggests they're simple options to be delivered to clients, without any special logic behind them. If that is really the case, it should be easy to implement.

For the initial implementation, we can ignore cases where DHCPv4 option is longer than 255 octets.