Add a "not applicable" reason for unspecified interested parties

[ScatteredInk]

For entities where an interested party is expected to be absent (e.g. a nation state), we may want a not-applicable entry in the unspecifiedReason codelist.

Alternatively, the current no-beneficial-owners entry could be updated to cover this and the expected absence of an interested party could be inferred from entity properties.

[kathryn-ods]

Alternatively, the current no-beneficial-owners entry could be updated to cover this and the expected absence of an interested party could be inferred from entity properties.

This is what is shown in scenario 3 of https://standard.openownership.org/en/latest/schema/guidance/repr-state-owned-enterprises.html closing as I think that resolves this

[kd-ods]

@kathryn-ods - let's leave this open (along with any other tickets tagged with 'feature: missing information'), since we'll want to review that set of tickets together as part of reviewing and addressing that feature.