Remove workaround for recovering users by username

Mapping the user ID into issued credentials is now stable. This workaround should be removed, and username no longer requested by default.

https://github.com/ADORSYS-GIS/keycloak-oid4vp-plugin/blob/222780864256d6dc9ee29045c822a9400d2141d4/src/main/java/io/github/adorsysgis/keycloak/protocol/oid4vc/oid4vp/authenticator/OID4VPAuthenticator.java#L271-L275

Consider also looking into enforcing the credential issuer for mDocs the same way it is done for SD-JWTs with respect to https://openid.net/specs/openid-4-verifiable-presentations-1_0.html#name-end-user-authentication-usi.

ETA: 2 days