Configuration updates to introduce optional backend weights to the haproxy configuration
Described in the design doc - https://docs.google.com/document/d/15jzLb5O4ASPYInxw1CFI-ngLHv2K8w01AuFOkejfcrk/edit#
We will want to have an option for all backends to introduce weights and also optionally include the canary hosts with a backend weight of zero.