Udp Proxy Fixed Attempted Upstream Host Tracking In Tunneling

Fixed missing attempted upstream host tracking in the :ref:UDP proxy <config_udp_listener_filters_udp_proxy> tunneling path. TunnelingConnectionPoolImpl now records the upstream host via StreamInfo::UpstreamInfo::addUpstreamHostAttempted on both pool ready and pool failure, so the %UPSTREAM_HOSTS_ATTEMPTED%, %UPSTREAM_HOST_NAMES_ATTEMPTED_WITHOUT_PORT% and related access log formatters are populated for tunneled (UDP-over-HTTP) sessions, matching the behavior of the non-tunneling UDP proxy and TCP proxy.