[Bug]: No protection for multiple PodAutoscalers targeting the same workload

[googs1025]

🐛 Describe the bug

There is currently no mechanism to prevent multiple PodAutoscaler resources from targeting the same underlying scalable workload (e.g., a Deployment, StormService).

This can result in:

• Multiple autoscalers concurrently writing to the same .spec.replicas field of the target resource.
• Unpredictable scaling behavior (e.g., one PA scales up, another scales down).

Steps to Reproduce

Specify two podautoscalers for the same workload

Expected behavior

The system should detect and reject any PodAutoscaler that targets a workload already controlled by another active PodAutoscaler.

Environment

aibrix: v0.4.1

[googs1025]

will fix this