Create role for custom instance user (#7635)

backend/migrations/20260120204751_custom_user_instance_createrole.down.sql

@@ -0,0 +1 @@
+-- Add down migration script here

backend/migrations/20260120204751_custom_user_instance_createrole.up.sql

@@ -0,0 +1,10 @@
+
+DO $$
+BEGIN
+  ALTER ROLE custom_instance_user CREATEROLE;
+EXCEPTION
+    WHEN others THEN
+        RAISE NOTICE 'Error in custom_instance_user migration: %', SQLERRM;
+        -- Continue without failing the migration
+END
+$$;