options: introduce the uri option as opposed to a string

options: introduce the uri option as opposed to a string

Currently we don't attempt to validate a uri given, aside from
not allowing any space characters within.

If the option is `array uri` then the first two bytes are the
length of the uri in network order and the rest is a uri element.
The uri's are space separated for the variable because space is not
allowed within the uri.

This allows us to implement RFC 8572, Secure Zero Touch Provisioning.