KIP-235 — Add DNS alias support for secured connection

Accepted Kafka 2.1 Security

Allows Kafka clients to resolve all A/CNAME records behind a DNS alias when using SASL/Kerberos, so the Kerberos service principal is constructed from the canonical hostname rather than the alias. When a DNS alias is listed in `bootstrap.servers`, the Java client performs Kerberos authentication against the alias string, which has no corresponding Kerberos service principal, causing `SaslException`.

Details