Reduce logging level when validating user certificates

[tanelkaar]

Currently validation iterates all trusted certs and tries to use them to validate user certificate. It it fails, the certificate content (which includes id-code and name) with WARN level and continues with the next one. As this pollutes logs with sensitive data, but is ignored during the process. The logging level should be DEBUG or lower.

Typical errors - EC certificate is first in the list and is used to validate "old" ESTEID2018 certificates.

Error verifying signer's certificate: SERIALNUMBER=PNOEE-XXXX, GIVENNAME=YYYY, SURNAME=ZZZZ, CN="YYYY,ZZZZ,WWWWWWWW", C=EE against CA certificate: CN=ESTEID2018, OID.2.5.4.97=NTREE-10747013, O=SK ID Solutions AS, C=EE

java.security.InvalidKeyException: Supplied key (sun.security.ec.ECPublicKeyImpl) is not a RSAPublicKey instance
.....

https://github.com/SK-EID/mid-rest-java-client/blame/master/src/main/java/ee/sk/mid/MidAuthenticationResponseValidator.java#L196