Add check "Tables are not linked to other tables"

[mfvanek]

See https://habr.com/ru/articles/803841/
Part "Отношения не участвующие в FK"
This check can find potentially outdated or unused tables

SELECT
	n.nspname,  -- схема
	t.relname   -- отношение
FROM pg_catalog.pg_class AS t
    INNER JOIN pg_catalog.pg_namespace AS n 
        ON t.relnamespace = n.oid
WHERE
    relkind IN ('r', 'p')
    AND t.oid NOT IN (SELECT conrelid FROM pg_catalog.pg_constraint WHERE contype IN ('f'))
    AND t.oid NOT IN (SELECT confrelid FROM pg_catalog.pg_constraint WHERE contype IN ('f'))
    AND n.nspname NOT IN ('information_schema', 'pg_catalog') 
    AND n.nspname NOT LIKE 'pg_toast%'