Add new nodes to an existing stack/cluster

- PUT (with positive scalingAdjustments) supported for stack and cluster resources
- flow for adding new instances to a stack and new hosts to a cluster
- AWS and Azure implementation of adding a new instance
- added a reusable PollingService to poll different resources with a timeout
Instead of using the same json object for multiple update operations we could use polymorphism. 
An example can be found in user handling (type hierarchy starting from the UpdateRequest interface)