Converting row elements into a arrays?

Postgresql 12.13

Given the sample below, I'm looking for how to generate this output.  It's
like GROUP BY, but generating an array instead of an aggreate number.
 f1 | f2_array
----+---------
1 | {1,2,3}
  2 | {1,2,3,4}
  3 | {1,2}

The ultimate goal is to somehow use pg_index.indkey to get column names from
pg_attribute.

create table foo (f1 int, f2 int);
insert into foo values (1, 1);
insert into foo values (1, 2);
insert into foo values (1, 3);
insert into foo values (2, 1);
insert into foo values (2, 2);
insert into foo values (2, 3);
insert into foo values (2, 4);
insert into foo values (3, 1);
insert into foo values (3, 2);

select * from foo order by f1, f2;
 f1 | f2
----+----
  1 |  1
  1 |  2
  1 |  3
  2 |  1
  2 |  2
  2 |  3
  2 |  4
  3 |  1
  3 |  2
(9 rows)

--
Born in Arizona, moved to Babylonia.