The previous fix prevented unintentional clearing of
`privacyPolicyUrl` and `maxAgeSeconds` by skipping the field
when its value was falsy, but this also removed the user's
ability to explicitly clear an existing value.
Move both fields into an `Additional Fields` collection so we
can distinguish between "not provided" (skip) and "provided
empty" (clear), matching the existing pattern in
`vendor/update.operation.ts`.
Signed-off-by: Émile Ré <emile@getprobo.com>
71cad5f15e