CASSANDRA-19669: Audit Log entries are missing identity for mTLS connections

[frankgh]

This patch adds the missing metadata from the authenticated user, which includes the identity for mTLS connections. Additionally, it notifies authentication failures during TLS handshake, for example when a client is attempting to authenticate with an expired certificate. This now will be recorded as a failed authentication attempt.

Patch by Francisco Guerrero; Reviewed by TBD for CASSANDRA-19669