Change program_challenge_serializer to shared_challenge_serialier using Panko::Serializer

First step : Change Program_challenge_serializer using Active_Model_Serializer to Shared_challenge_serializer using Panko::Serializer

Add attributes

Add delegate

Changes index_challenges into Programs_controller file to call the new serializer.

TODO:

Def programs method to call challenge.program.id info and display them in the serializer.

then clean file from commented lines.

Part of the issue 695