How to set statistics level of a table in postgres?
There is nothing ready-made for a table or schema, because that is seldom useful.
But you can set it for a whole database with
ALTER DATABASE mydb SET default_statistics_target = 1000;

You can also use psql's \gexec to set the statistics target for all columns of a table:
SELECT format(
          'ALTER TABLE %s ALTER %I SET STATISTICS 1000',
          attrelid::regclass,
          attname
       )
FROM pg_attribute
WHERE attrelid = 'pgbench_tellers'::regclass
  AND attnum &gt; 0 \gexec