Backport of fix: add skip_exit to drain_listeners to prevent premature pod termin… into release/1.8.x

.changelog/1064.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+- envoy: add `skip_exit` to `drain_listeners` admin API call to prevent premature pod termination when upgrading to Envoy 1.37+
+```

pkg/envoy/proxy.go

@@ -177,7 +177,7 @@
 // Note: the caller is responsible for ensuring Drain is not called concurrently
 // with Run, as this is thread-unsafe.
 func (p *Proxy) Drain() error {
-	envoyDrainListenersUrl := fmt.Sprintf("http://%s:%v/drain_listeners?inboundonly&graceful", p.cfg.AdminAddr, p.cfg.AdminBindPort)
+	envoyDrainListenersUrl := fmt.Sprintf("http://%s/drain_listeners?inboundonly&graceful&skip_exit", net.JoinHostPort(p.cfg.AdminAddr, strconv.Itoa(p.cfg.AdminBindPort)))
 	switch p.getState() {
 	case stateExited:
 		// Nothing to do!