ComputeDomain: add support for elastic workloads #349
Description
The workload in a ComputeDomain (CD) may change size over time (think: growing/shrinking ReplicaSet, Job, JobSet, ...). The CD should then adhere to the philosophy of following the workload and dynamically shrink and expand as needed, too. Today, that means for example to dynamically add/remove nodes to/from that CD, respectively.
This is strongly related to #348 and potentially the same implementation will enable both.