add --sequence-data to pg_dumpall

I noticed that I forgot to add --sequence-data to pg_dumpall in commit
9c49f0e, which added the same option to pg_dump. This option is primarily
intended for use by pg_upgrade, so we will need it if/when we teach
pg_upgrade to use pg_dumpall to dump the databases. (Right now pg_upgrade
directly calls pg_dump on each database.)

Assuming we want this patch, should we apply it to v18? It's arguably an
oversight in the pg_dump --sequence-data commit, and pg_dumpall will just
pass the option through to pg_dump, but otherwise there's not a really
strong reason it can't wait.

--
nathan