Change the method for creating a user's full name from OIDC tokens

Currently we're populating the user's full name with "{firstname} {lastname}" (probably somewhere during authentication), but probably it would be better to use "{lastname}, {firstname}" because that format is expected in the record metadata (and transforming names from one format into the other is error-prone, c.f. #8 (closed)).

AFAIK, the first and last name are reported in separate claims in OIDC tokens anyway.