Refactor JSON templates to be generated with ActiveModelSerializers instead of Rabl (#4090)

app/serializers/rest/application_serializer.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class REST::ApplicationSerializer < ActiveModel::Serializer
+  attributes :id, :name, :website, :redirect_uri,
+             :client_id, :client_secret
+
+  def client_id
+    object.uid
+  end
+
+  def client_secret
+    object.secret
+  end
+end