Store capybara-screenshots as build artifacts

Locally, when a Capybara test fails, capybara-screenshot stores the response body (and sometimes a screenshot) in tmp/capybara.

We disabled this when in a CI environment because at the time we didn't have a way to view them. But now with build artifacts I'm wondering if that's no longer the case.

@ayufan Is it possible to make these available as build artifacts? What would we need to do? We can change the output directory.

I think it would sometimes be helpful to figure out why a spec fails on CI.