Revert "Revert "Rate-limit assets.digital.cabinet-office.gov.uk""
Revert "Revert "Rate-limit assets.digital.cabinet-office.gov.uk""

This reverts commit 3592d0816b443a5844a00b3e4843d33b9cb9dd8c.

We can safely rate-limit on the assets virtual host now that Nginx is
able to distinguish between the client IP addresses due to the change in
commit 656b4ca.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet