[CAEP] Credential Change event needs structure

[timcappalli]

credential_type and then all credential specific properties need to be part of a structure data model (x509_issuer, x509_serial, fido2_aaguid)

Might want to use AMR claim as a reference.

[timcappalli]

on 2023-03-21: needs more discussion on next call with larger audience

[tulshi]

Since this event is already in use by a few companies, how should we address this concern such that we don't break their implementations?