Fold all conditions into the pending workload query

[julik]

When we autoscale based on queue depth, and use scheduler keys and fuses, we want to take into account all the conditions. The idea has two benefits:

• We should have only 1 scope for selecting the next workload, without having it double. It should be sufficiently efficient to be usable in both contexts (autoscaler metric and dequeue)
• When we autoscale, the fuses should have effect on that autoscaling. If we fuse out 80% of the workloads, there is no point running 80% of compute allocated to those workloads in the anticipation that they are going to become needed once we de-fuse the workloads back in.

Same for scheduler keys - it is possible to know which scheduler keys are currently known to the system, and there is no reason removed scheduled workloads should still influence the autoscaler.

This is WIP, as we need a decent benchmark which allows us to tweak this scope/query with a realistic queue size matching our real-life setup.