Fix scaling policy

[gustavderdrache]

This PR addresses a missing resource label required for request count-based scaling. It does a little bit of ARN (Amazon Resource Name) shuffling, so there are a few pieces in play, but ultimately the activity is fairly minimal:

1. It exposes the load balancer's ARN for consumption by Drupal deployments.
2. The Drupal deployment uses both the load balancer and target group ARNs to construct a resource label as required by the ResourceType field in the API.

Since there's a bit of commentary and code added for the ARN manipulating, the scaling policies have been moved into a new file, hence the extra diff noise.