Allow overriding the adapter with render option

Make it easy to use multiple adapters in an app.

use "adapter: false" to not use ams

make a test override config.adapter

test/serializers/configuration_test.rb

@@ -7,7 +7,7 @@ module ActiveModel
         assert_equal ActiveModel::Serializer::ArraySerializer, ActiveModel::Serializer.config.array_serializer
       end
 
-      def test_adapter
+      def test_default_adapter
         assert_equal :json, ActiveModel::Serializer.config.adapter
       end
     end