pkg/proxy: add last-queued-timestamp metric

This adds a metric, kubeproxy_sync_proxy_rules_last_queued_timestamp,
that captures the last time a change was queued to be applied to the
proxy. This matches the healthz logic, which fails if a pending change
is stale.

This allows us to write alerts that mirror healthz.

Signed-off-by: Casey Callendrello <cdc@redhat.com>

pkg/proxy/winkernel/proxier.go

@@ -736,6 +736,7 @@ func getHnsNetworkInfo(hnsNetworkName string) (*hnsNetworkInfo, error) {
 func (proxier *Proxier) Sync() {
 	if proxier.healthzServer != nil {
 		proxier.healthzServer.QueuedUpdate()
+		metrics.SyncProxyRulesLastQueuedTimestamp.SetToCurrentTime()
 	}
 	proxier.syncRunner.Run()
 }