fix : certain db level settings in duckdb can't be set again

[k-anshul]

This is just a fix for release blocker. The permanent solution will be as follows:

1. Most of our settings are global configuration except max_expression_depth.
2. It seems extensions are now loaded at db level and not connection level. The following code now works:

	_, err = conn1.ExecContext(context.Background(), "INSTALL spatial; LOAD spatial;")
	if err != nil {
		log.Fatal(err)
	}

	row := conn2.QueryRowContext(context.Background(), "SELECT ST_Area('POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))'::GEOMETRY);")
	var area float64
	err = row.Scan(&area)
	if err != nil {
		log.Fatal(err)
	}
	log.Println(area)

3. Introduce two new options in rduckdb :
   a. DBInitQueries : Runs for db handle once. Extensions, global configurations and init_sql in connector config will be DBInitQueries.
   b. ConnInitQueries: Runs for each connection. Local configurations will be ConnInitQueries.
4. After opening DB run DBInitQueries.
5. Run ConnInitQueries before returning a read or write connection.