Messenger user id (the page-scoped user id). We Need to forward it to Meta

Meta conversions adapter (POST /v1/ads/conversions) already sends messaging_channel at the event root when the action source is business_messaging. It supports whatsapp, messenger and instagram_direct, and for Messenger/Instagram it puts the page_id in user_data. The part that's missing is the Messenger user id (the page-scoped user id). We don't forward it to Meta right now, so there's no way to pass it through us today.