turbopack: parse and propagate `output: 'export'` (#48046)
Depends on https://github.com/vercel/turbo/pull/4491
This adds support for the new `output: 'export'` configuration, and
propagates the value through to our Node.js rendering code to render.
Unfortunately, we don't support page-level configs at the moment, so we
can't set a `export const config = { dynamic: 'force-dynamic' }` and
test that the export value is being received (I've manually verified it,
though).
Fixes WEB-842
