Add linter to check for jsonb_set to avoid setting NULL

[RyanSquared]

20:44 lee=# select jsonb_set('{"foo":"aaaaaa","bar":[444, 555, {"test": false, "failed": 1}]}'::jsonb, '{foo}', NULL);
20:44 jsonb_set
20:44 -----------

The usage of NULL rather than 'null'::jsonb clears out the JSON values.

[RyanSquared]

This would have to be not a literal NULL check but instead ensure either a literal value or a coalesce(<input here>, 'null'::jsonb)