Add CDB_Username() function

test/CDB_Username.sql

@@ -0,0 +1,17 @@
+SELECT current_user; -- postgres
+SELECT CDB_Username(); -- (NULL)
+
+-- Connect with admin
+\set QUIET on
+\o log/test.log
+SELECT current_database() AS current_database;
+\gset
+SELECT SUBSTRING (:'current_database', 19, 36) AS user_id;
+\gset
+SELECT rolname AS admin_user FROM pg_roles where rolname LIKE ('%' || :'user_id');
+\gset
+\c :current_database :admin_user
+\o
+\set QUIET off
+
+SELECT CDB_Username(); -- admin