[db-wg] phone number required for person objects

Hi,

TL;DR: stop requiring the "phone" attribute for person objects.

This is something that I quickly brought up during the db-wg session
at RIPE84 but thought would be good to bring up here as well.

Currently you need to specify a phone number for person objects but
not for role objects, which I think should be fixed (as in not require
it for person objects either).

While there is the argument to be made to not encourage use of person
objects or whatever, I do think that we should make sure that they are
functionally the same as to prevent people putting PII in role
objects.

This is so we can still keep track of how many personal contact
objects there are, which would be more difficult if people used role
objects for personal contacts.

-Cynthia