MINOR: server: add log on dynamic server creation

Add a notice log to report the creation of a new server. The log is
printed at the end of the function.
diff --git a/src/server.c b/src/server.c
index ac53221..e8cbdee 100644
--- a/src/server.c
+++ b/src/server.c
@@ -4457,6 +4457,7 @@
 
 	thread_release();
 
+	ha_notice("New server %s/%s registered.\n", be->id, srv->id);
 	cli_msg(appctx, LOG_INFO, "New server registered.");
 
 	return 0;