Adding a (failing) test case for inserting to table with generated columns

[legezam]

This new test case is for demonstrating the issue with type provider.

The issue is basically this: If you are trying to insert a row to a table with generated columns, even if you don't supply value for the generated column, the type provider attempts to insert to that column. At least the error i get suggests that:

42601: cannot insert into column "result"

table def:

--
-- Name: table_with_computed_columns; Type: TABLE; Schema: public; Owner: postgres
--

CREATE TABLE public.table_with_computed_columns (
    id integer NOT NULL,
    operand_1 integer NOT NULL,
    operand_2 integer NOT NULL,
    result integer GENERATED ALWAYS AS ((operand_1 * operand_2)) STORED
);