WITH 
product AS (
      SELECT 1 AS id, 'ласты' AS name, 4 AS cat_id
UNION SELECT 2 AS id, 'тапки' AS name, 4 AS cat_id
UNION SELECT 3 AS id, 'коньки' AS name, 4 AS cat_id
UNION SELECT 4 AS id, 'лыжи' AS name, 2 AS cat_id
UNION SELECT 5 AS id, 'палатка' AS name, 2 AS cat_id
),
cat AS (
      SELECT 4 AS id, 'товары для дома' AS name
UNION SELECT 2 AS id, 'скобяные товары' AS name
UNION SELECT 1 AS id, 'пендык' AS name
)

SELECT *,
       (SELECT jsonb_agg(row_to_json(t2.*)) FROM product t2 WHERE t2.cat_id = t1.id) AS jsonb
FROM cat t1;