Refactor all ActivityPub deliveries to be serialized and signed through one concern (#10966)

app/services/concerns/payloadable.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Payloadable
+  def serialize_payload(record, serializer, options = {})
+    signer    = options.delete(:signer)
+    sign_with = options.delete(:sign_with)
+    payload   = ActiveModelSerializers::SerializableResource.new(record, options.merge(serializer: serializer, adapter: ActivityPub::Adapter)).as_json
+
+    if (record.respond_to?(:sign?) && record.sign?) && signer && signing_enabled?
+      ActivityPub::LinkedDataSignature.new(payload).sign!(signer, sign_with: sign_with)
+    else
+      payload
+    end
+  end
+
+  def signing_enabled?
+    true
+  end
+end