Validate a serialized Supply Chain Object string

Checks that one serialized supply chain object (SCO) is well formed, without verifying the entities it declares. Send the serialized SCO string as sco. The response reports a status of valid, invalid, or error and, where the SCO cannot be accepted, the reasons codes for it: the SCO declaring an incomplete chain (101) or the string failing to deserialize (102). No seller records are consulted, so authorization problems are not reported here — use the validate-and-verify endpoints for those.