Add E2EE API (#13820)

app/serializers/rest/encrypted_message_serializer.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class REST::EncryptedMessageSerializer < ActiveModel::Serializer
+  attributes :id, :account_id, :device_id,
+             :type, :body, :digest, :message_franking
+
+  def id
+    object.id.to_s
+  end
+
+  def account_id
+    object.from_account_id.to_s
+  end
+
+  def device_id
+    object.from_device_id
+  end
+end