Avoid an nginx timeout on the redemption endpoint

PaymentServer is expected to take up to 600s to respond to some redemption requests. The default nginx 60s timeout preempts this and returns a worse error response to clients.

This tells nginx to wait longer than PaymentServer before timing out any /v1 response. This is strictly more of a change than I want but I also don't want to start hard-coding a lot of specific detail about the PaymentServer API into the nginx configuration.