Add disclaimer and changelog entry for Person.identifier

[duncandewhurst]

Person.identifier was added in #427 in pursuit of alignment with the OCDS Beneficial Owners extension. However, we omitted adding a disclaimer like the one in the extension documentation:

to use this extension, the laws in your jurisdiction must permit the publication of personal identifiers.

I think that we should add a similar disclaimer to the reference documentation for the Person subschema.

To reduce the chances of implementers unnecessarily publishing personal identifiers, I think that we should also include a clarification that Person.identifer is only relevant in the context of Organization.beneficialOwners (the Person subschema also appears in the context of Organization.people, relating to the CoST IDS element 'Contract officials and roles', for which personal identifiers are not relevant).

At the same time, we can update the changelog entry for #427, which presently only mentions Organization.beneficialOwners, to include Person.identifier and the other fields added to the Person subschema.

@jpmckinney sound good?

[jpmckinney]

Sounds good