Add placeholder functions for "repmgr $command --help"

There are now too many options to sensibly fit into general --help
output; we'll add separate output for each repmgr command, e.g.
"repmgr node --help".

repmgr-action-node.c

@@ -1249,11 +1249,7 @@ do_node_check_downstream(PGconn *conn, OutputMode mode, CheckStatusList *list_ou
 	return status;
 }
 
-// --action=...
-// --check
-// --list -> list what would be executed for each action, filter to --action
 
-// --checkpoint must be run as superuser - check connection
 void
 do_node_service(void)
 {
@@ -1967,3 +1963,12 @@ copy_file(const char *src_file, const char *dest_file)
 
 	return true;
 }
+
+
+void
+do_node_help(void)
+{
+	print_help_header();
+
+
+}