CORE-5832 Removed more "success", "status", and "action" keys from JSON responses.
CORE-5832 Removed IDs from Pipeline JSON steps.

Pipeline endpoints now use the JSON array index to refer to source and target steps in the mapping JSON, so the client is no longer required to generate UUIDs for new steps.
The step UUIDs have also been removed from the step JSON objects, since they are no longer used in the mapping JSON.