The change from `db/schema.rb` to `db/structure.sql` requires `pg_dump`,
which can fail if the `pg_dump` version used is older than the
PostgreSQL server that is running.

We now disable schema dumping after migrations for production;
development still does this by default. This can be invoked directly via
`rake db:schema:dump`.

This should address
https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5299.