pgduck client: include conninfo in start-failure error

Add an errdetail() clause to the "could not start query engine"
ereport() so users can see which connection string was being used
when the connection to pgduck_server failed.

Issue: #293
Signed-off-by: David Christensen <david.christensen@snowflake.com>

Author: sfc-gh-dachristensen

pg_lake_engine/src/pgduck/client.c

@@ -144,10 +144,14 @@ GetPGDuckConnection(void)
 		PQfinish(connection);
 
 #ifdef USE_ASSERT_CHECKING
-		ereport(ERROR, (errmsg("could not start query engine: %s", errorMessage)));
+		ereport(ERROR,
+				(errmsg("could not start query engine: %s", errorMessage),
+				 errdetail("connection string: %s", PgduckServerConninfo)));
 #else
 		/* hide internals from users */
-		ereport(ERROR, (errmsg("could not start query engine")));
+		ereport(ERROR,
+				(errmsg("could not start query engine"),
+				 errdetail("connection string: %s", PgduckServerConninfo)));
 #endif
 	}