time values when batch issuing credentials

[TimoGlastra]

We should take into account that the iat, exp etc.. claims in batch issuance can be correlating. Not sure if we can provide APIs for this in credo, or whether it's an consideration to mention in the docs.

E.g. one could round down all times to midnight, meaning that all credentials issued on the same day will have the same iat/exp. But this is dependant on business logc