[v16] Mark Discovery service healthy on startup (#43283)

* Mark Discovery service healthy on startup

* bump e

lib/service/discovery.go

@@ -128,6 +128,11 @@ func (process *TeleportProcess) initDiscoveryService() error {
 	}
 	logger.InfoContext(process.ExitContext(), "Discovery service has successfully started")
 
+	// The Discovery service doesn't have heartbeats so we cannot use them to check health.
+	// For now, we just mark ourselves ready all the time on startup.
+	// If we don't, a process only running the Discovery service will never report ready.
+	process.OnHeartbeat(teleport.ComponentDiscovery)(nil)
+
 	if err := discoveryService.Wait(); err != nil {
 		return trace.Wrap(err)
 	}