[FEATURE]: Give users ability to write custom Routing logic in Python

### Feature request

This is already done here #2798. Opening this issue just to track this feature.

Docs
https://github.com/ai-dynamo/dynamo/blob/main/docs/architecture/kv_cache_routing.md#custom-routing-example-minimizing-ttft

### Describe the problem you're encountering

N/A

### Describe alternatives you've tried

_No response_