Add administrative webhooks (#18510)

* Add administrative webhooks

* Fix error when webhook is deleted before delivery worker runs

app/services/webhook_service.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+class WebhookService < BaseService
+  def call(event, object)
+    @event  = Webhooks::EventPresenter.new(event, object)
+    @body   = serialize_event
+
+    webhooks_for_event.each do |webhook_id|
+      Webhooks::DeliveryWorker.perform_async(webhook_id, @body)
+    end
+  end
+
+  private
+
+  def webhooks_for_event
+    Webhook.enabled.where('? = ANY(events)', @event.type).pluck(:id)
+  end
+
+  def serialize_event
+    Oj.dump(ActiveModelSerializers::SerializableResource.new(@event, serializer: REST::Admin::WebhookEventSerializer, scope: nil, scope_name: :current_user).as_json)
+  end
+end