Add optional check for unsupported future PostgreSQL releases

This is for backbranches to prevent them running against newer
PostgreSQL versions with which they are not compatible, for example
4.4.x with PostgreSQL 12 and later.

repmgr-action-standby.c

@@ -1081,6 +1081,9 @@ _do_create_replication_conf(void)
 	/* check connection */
 	source_conn = establish_db_connection_by_params(&source_conninfo, true);
 
+	/* Verify that source is a supported server version */
+	(void) check_server_version(source_conn, "source node", true, NULL);
+
 	/* determine node for primary_conninfo */
 
 	if (runtime_options.upstream_node_id != UNKNOWN_NODE_ID)