Adding support for batched provisioning

[sahan-ctds]

Description

This PR adds optional batch provisioning support to Fallout, allowing NodeGroups to be provisioned in sequential batches instead of all in parallel. This feature helps prevent resource exhaustion (e.g., memory, CPU) when provisioning many NodeGroups simultaneously.

This PR introduces a new optional system property fallout.system.provisioning.batch_size that allows users to control how many NodeGroups are provisioned simultaneously. When configured, NodeGroups are divided into batches and provisioned sequentially:

1. NodeGroups within a batch provision in parallel
2. Each batch waits for completion before the next batch starts
3. If any batch fails, subsequent batches are skipped

Format:

ensemble:
  fallout.system.provisioning.batch_size: 5
  servers:
    ...
  clients:
    ...
  observer:
    ...

Changes

1. FalloutPropertySpecs.java: Added provisioningBatchSizePropertySpec property definition
2. Ensemble.java:
   • Added provisioningBatchSize field and getter
   • Added transitionStateWithFunction() method to support batch processing with per-NodeGroup state determination
   • Modified transitionState() to implement batch logic for uniform state transitions
3. EnsembleBuilder.java: Added batch size field and builder method
4. ActiveTestRunBuilder.java: Added YAML parsing for batch size property
5. ActiveTestRun.java: Modified transitionEnsembleStateUpwards() to use ensemble-level batch-aware transitions