Update an entity with the provided details, then associated it with a parent organisation, or update any existing association.
To use an existing entity, and not update it, either omit the entity field, use null, or just provide an entity object that
contains only the entity ID, which must match the one given in the request URL.
At least the entity name (family name for individuals, registered name for organisations) must be present in the entity after
any update.
The referenced parent entity must be of type ORGANISATION and an ownership query must have been previously completed.
At least one of role or percentage held must be in the request. If either is null or omitted, then any existing details will
be retained. If either detail is given, the it will be replaced, not merged.