Return Error Content if validation fails

[LasneF]

current behaviour when there is a validation error is that it returns a 502

the enhancement i propose is that the returned payload contains a structured error containning this list of failures , as well as the payload

this allow to have an off line diagnotics without the usuage of the (nice) UI

context of usage beeing newman + wiretap in CICD

given the fact that in case of error newman log the payload, it allows to understand that there was an error, and then to diagnose

it may requires a dedicated flag