DRS improvements

### The required feature described as a wish

As a Operator I would like to have the loads on my systems more evenly/centrally distributed. At the moment there is a simple DRS for clusterwide distribution of loads, this is however not applying zone wide distribution or based on automated queries/improvements.

In addition we should add historic data for the VM in planning possible migrations.
At the moment allocated metrics are used. An first improvement would be to use actual metrics.

Start by understanding CloudStack’s existing clusterwide DRS behavior and the operator’s desired zone-wide distribution. Clarify how automated queries or improvements should work, and whether historical actual VM metrics replace allocated metrics; done requires concrete, testable requirements for all three areas.

Written by the indexing model from the issue text.