Tweak extension configuration

repmgr--4.0.sql

@@ -0,0 +1,7 @@
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION repmgr" to load this file. \quit
+
+CREATE TABLE nodes (
+  node_id          INTEGER PRIMARY KEY,
+  type             TEXT    NOT NULL CHECK (type IN('master','standby','witness','bdr'))
+);