Changes to Get a single Custom Activity instance

added the pattern property ^custom\.(cf|lcf|ccf|acf|gcf|scf)_[A-Za-z0-9]+$ to the response body for the status 200

added the media type application/json for the response with the status 400

added the media type application/json for the response with the status 401

added the media type application/json for the response with the status 404

added the non-success response with the status 403

added the non-success response with the status 429

added the optional property created_by_agent_id to the response with the 200 status

added the optional property updated_by_agent_id to the response with the 200 status

added the new optional query request parameter _fields