Fallback rules for GovStore/Digital Marketplace paths

These rules are for:
  `/cloudstore/supplier/*`,
  `/cloudstore/service-id`,
  `/cloudstore/category/service-id`,
  `/cloudstore/category/sub-category/service-id` and
  `/cloudstore/category/sub-category/sub-sub-category/service-id`.
As discussed, I think our lines are getting long here. Also as discussed, I'm happy to merge as-is.

As a matter of personal taste rather than a prerequisite for merge I'd prefer:

```ruby
      elsif request.host == 'govstore.service.gov.uk'
        case request.path
          when %r{^/cloudstore/supplier/}
            redirect("https://www.gov.uk/digital-marketplace")
          when %r{^/cloudstore/([_0-9a-zA-Z-]+)$}
            redirect("http://www.digitalmarketplace.service.gov.uk/service/#{$1}")
          when %r{^/cloudstore(/[ips]aas|/scs)(/[_0-9a-zA-Z-]+){0,2}/([_0-9a-zA-Z-]+)$}
            redirect("http://www.digitalmarketplace.service.gov.uk/service/#{$3}")
        end
      end
```

... but I acknowledge this is Not How We've Done It Above :smile: