accommodate new historical_identity_state property on OIDF fetch endpoint

[jchartrand]

We'll need to make sure the forthcoming historical_identity_state property on the OIDF /fetch endpoint (as described at digitalcredentials/dcc-members-oidf#64) is properly passed through when it comes back through the issuer-registry-client (see digitalcredentials/issuer-registry-client#13)

See also:

• use did history from new historical_identity_state property on OIDF fetch endpoint verifier-plus#264